Rational L‐space surgeries on satellites by algebraic links

Given an n ‐component link L in any 3‐manifold M , the space L⊂(Q∪{∞})n of rational surgery slopes yielding L‐spaces is already fully characterized in joint work by the author when n=1 and L is nontrivial. For n>1 , however, there are no previous results for L as a rational subspace, and only limited results for integer surgeries L∩Zn on S3 . Herein, we provide the first nontrivial explicit descriptions of L for rational surgeries on multi‐component links. Generalizing Hedden's and Hom's L‐space result for cables, we compute both L , and its topology, for all satellites by torus‐links in S3 . For fractal‐boundaried L resulting from satellites by algebraic links or iterated torus links, we develop arbitrarily precise approximation tools. We also extend the provisional validity of the L‐space conjecture for rational surgeries on a knot K⊂S3 to rational surgeries on such satellite‐links of K . These results exploit the author's generalized Jankins–Neumann formula for graph manifolds.


Introduction
A connected, closed, oriented 3-manifold is called an L-space if its reduced Heegaard Floer homology vanishes. The present work focuses on the following relative notion of L-space. The author's joint result with Rasmussen [28] characterizing nontrivial L for knot exteriors in 3-manifolds led both to our toroidal gluing theorem for L-spaces [28] and to the author's independent proof of the L-space conjecture for graph manifolds [29]. Our joint work on L combined with Hanselman and Watson's studies of combinatorial properties of certain bordered Floer algebras [16] gave rise to a topological realization of bordered Floer homology for single-torus boundaries [15]. A multiple-boundary-component version of this should also exist.
Methods: Classification formula. Despite reliance on an enhanced L-space gluing tool proved in Theorem 3.6, † this paper was primarily made possible by the author's classification of graph manifolds admitting co-oriented taut foliations, with proof of the graph-manifold Lspace conjecture as by-product [29]. (This is not to be confused with the author's joint work with Hanselman et al [14].) ‡ This classification combines a new classification formula (Theorem 4.3), generalizing that of Jankins and Neumann for Seifert fibered spaces [19], with a structure theorem (Theorem 4.4) prescribing the interpretation of outputs of this formula.
This classification tool also governs L-space regions for unions of graph manifolds with single-torus-boundary manifolds. In particular, it gives a complete abstract characterization of L for any graph-manifold-exterior satellite of any knot in any 3-manifold. The classification formula alternately composes a linear-fractional transformation φ P e * , induced by a gluing map φ e for each edge e, with a pair y v ± , for each vertex v, of extremizations of locally finite collections of piecewise-constant functions of slopes in a certain Seifert-data-compatible basis.
Results. Herein, we analyze the intricate behavior of solutions L to the classification formulae for exteriors of such satellites. The bounded-chaotic behavior of these y v ± generically leads to fractal-boundaried L, but we develop precise tools for local approximation and topological characterization. As sample applications of these tools, Theorems 1.6 and 1.7 construct global inner approximations of L for satellites by algebraic links and iterated-torus-links, respectively.
Moreover, for a satellite in S 3 by an n-component torus link, the chaotic behavior of y v ± generically degenerates, and we provide an exact explicit description of L and its various possible topologies, in Theorems 1.2 and 1.3, respectively. Finally, in Theorem 1.4 and Corollary 1.5, we promote L-space conjecture results for knot surgeries to results for satellite surgeries.

Torus-link satellites
The T (np, nq)-torus-link satellite K (np,nq) ⊂ M of a knot K ⊂M in a 3-manifold M embeds the torus link T (np, nq) in the boundary of a neighborhood ν(K) of K ⊂M . The exterior Y (np,nq) of K (np,nq) splices K ⊂M to the multiplicity-q fiber of the Seifert fibered exterior of T (np, nq). This Seifert structure also prescribes three distinguished subsets Λ, R, Z ⊂ n i=1 P(H 1 (∂ i Y (np,nq) )) of slopes. The lattice Λ acts on slopes by reparametrization of Seifert data, and R \ Z catalogs reducible surgeries with no S 1 × S 2 connected summand. (ii) if 2g(K) − 1 q p , and K ⊂ S 3 is nontrivial, or if p, q > 1 and K ⊂ S 3 is the unknot (so that K (np,nq) = T (np, nq)), then for N pq := pq − p − q + 2g(K)p, we have Remarks. Positive L-space knots K ⊂ S 3 have L S 3 = [2g(K)−1, +∞] [27]. Theorem 4.5 and its remark cover the remaining (redundant or less interesting) cases of negative L-space or non-L-space knots K, and the fractal-boundaried case of K (np,nq) = T (n,nq) (for p = 1 and K the unknot). for K ⊂ S 3 a nontrivial positive L-space knot with 2g(K) − 1 q p , and (i) L S 3 (Y (p,q) ) = {∞} for 2g(K) − 1 > q p , recovering well-known results of Hedden [17] and Hom [18] for cables.

Topology of L(Y (np,nq)
). An appropriate real completion L R of L has interesting topology.
We briefly pause here to elaborate on the distinguished subsets R, Z, B, and Λ of sf-slopes.
The action of Λ induces homeomorphism on Dehn surgeries: S 3 l·α (K (np,nq) ) ∼ = S 3 α (K (np,nq) ) for l ∈ Λ(Y (np,nq) ) and α ∈ (Q ∪ {∞}) n S 3 . Thus Λ preserves R, Z, B, L, and N L as sets, and since S 3 L * (K (np,nq) ) ∼ = S 3 L (K (np,nq) ), L * S 3 completely catalogs the L-space surgeries on K (np,nq) . The L-space surgery slopes for K (np,nq) must retain their full Λ-orbits, but sf-slopes do this automatically: the expression of L sf (Y (np,nq) ) in Theorem 4.5 is naturally Λ-invariant. Moreover, L * S 3 (Y (np,nq) ) is almost Λ-invariant. When L * S 3 = {∞}, L S 3 \ L * S 3 is given by For any K (np,nq) in Theorem 1.2, the Λ-mismatch L S 3 \ L * S 3 lies inside a radius-1 neighborhood, {α| α i = pq}, and L S 3 consists of a finite union of rectangles outside any positive-radius neighborhood of R S 3. Moreover, (8) implies the integer slopes in L S 3 (Y (np,nq) ) satisfy and it is a simple exercise to determine α ∈ (L S 3 \ L * New features: Torus-link satellites versus One-strand Cables. L-space regions for satellites by n > 1 torus links introduce qualitatively new phenomena not present for n = 1 cables. (a) For n > 1, the action of Λ becomes nontrivial, although as discussed before, this action does not impact actual L-spaces resulting from surgery.
(b) For n > 1, the codimension-1 subspace R S 3 ⊂ (Q ∪ {∞}) n S 3 acquires positive dimension and the codimension-2 subspace Z S 3 ⊂ (Q ∪ {∞}) n S 3 becomes nonempty, although the set of reducible L-space slopes R S 3 \ Z S 3 remains a disjoint union of hyperplanes ∼ = Q n−1 for all n.

The L-space Conjecture
The L-space conjectures, stated formally by Boyer-Gordon-Watson [5] and Juhász [20], posit the existence of left-invariant orders on fundamental groups and of co-oriented taut foliations, respectively, for all prime, compact, oriented non-L-spaces.
One might notice that our sharper results here lie in case (i) 2g(K) − 1 > q p of Theorem 1.2. While this case is the less interesting one from the standpoint of L-space production, it is the more nontrivial one from the standpoint of the L-space conjecture, since in this case every non-S 3 surgery on K (np,nq) has nontrivial reduced Heegaard Floer homology.
For the 2g(K) − 1< q p case, the difficulty with slopes α ∈ ([−∞, N pq > n \[−∞, N pq − p > n ) is that the existence of a CTF on Y (np,nq) (α) depends on the family of suspension foliations on ∂Y -necessarily of nontrivial holonomy -that arise from taking a CTF F of slope 2g(K) − 1 on Y and restricting F to ∂Y . Such F can only be extended over the union Y (np,nq) if it matches with the boundary restriction of some CTF of sf-slope p * −Nq * q−Np on the Seifert fibered space glued to Y to form the satellite. A similar phenomenon occurs for LOs on the fundamental group of Y (np,nq) (α). See Boyer and Clay [4] for more on this subtlety in gluing behavior.
In Theorem 8.1 of Section 8, we prove a result analogous to the one above, but for satellites by algebraic links or iterated torus-links. Instead of restating this theorem here, we state a: In [28], Rasmussen and the author conjectured that our L-space gluing theorem (see Theorem 3.5) also holds without the hypothesis of admitting more than one L-space Dehn filling. Hanselman, Rasmussen, and Watson recently announced a proof of this conjecture in [15], implying that the above corollary also holds for any non-L-space knot K ⊂ S 3 .

Satellites by algebraic links
In the context of negative definite graph manifolds, the distinction between L-space and non-L-space has consequences for algebraic geometry.
Némethi recently showed that the unique negative-definite graph manifold Link(X, •) bounding the germ of a normal complex surface singularity (X, •) is an L-space if and only if (X, •) is rational [24]. Due to results of the author in [29], we can promote this statement to a relative version: the subregion L nd ⊂ L(Y Γ ) of negative-definite L-space Dehn filling slopes for a graph manifold Y Γ parameterizes, up to equisingular deformation, the rational surface singularities (X, •) admitting 'end curves' (C, •) ⊂ (X, •) (see [25]), such that Link(X \ C) = Y Γ . If one such (X, •) is (C 2 , 0), then Y Γ is the exterior of an algebraic link, motivating the following study.
Setup. Although a T (np, nq)-satellite operation is specified by (an unknot complement in) the Seifert fibered exterior of T (np, nq) determined by the triple (p, q, n), a sequence of torus-linksatellite operations is specified by a rooted tree Γ determining the graph manifold exterior of the pattern link, where each vertex v ∈ Vert(Γ) specifies the Seifert fibered and λ v 0 of respective multiplicities p v and q v , and components of T v are regular fibers in S 3 v . Since we direct the edges of Γ rootward, each vertex w has a unique outgoing edge e w , corresponding to the incompressible torus in whose neighborhood T w is embedded, or equivalently, to a gluing map φ ew splicing the multiplicity-q w fiber λ w 0 ∈ S 3 w to a Seifert fiber in S 3 u , for u := v(e w ), where we write v(e) to denote the vertex on which an edge e ∈ Edge(Γ) terminates. (A 'splice' is a type of toroidal connected sum exchanging meridians with longitudes.) There are only two types of fiber in S 3 u available for splicing: a regular fiber, which we then regard as one of the Since this latter splice could be redefined as a smooth one if p u = 1, we demand p u > 1 without loss of generality.
If we define J v ⊂ j(E in (v)) and its complement I v by then I v catalogs the boundary components of Y v left unfilled, forming the exteriors of link components, so that the total satellite K Γ ⊂ S 3 of K ⊂ S 3 has v∈Vert(Γ) |I v | components. The pattern link specified by Γ is then an algebraic link if and only if its graph manifold exterior is negative definite, which, by straightforward calculations as appear, for example, in Eisenbud and Neumann's book [8], is equivalent to the condition that Γ is a tree, and that Conversely, given an isolated planar complex curve singularity (•, C) → (0, C 2 ), one can obtain such a tree Γ from Newton-Puisseux expansions for the defining equations of C, or alternatively from the amputated splice diagram of the dual plumbing graph of X for a good embedded resolution ( X, C) → (C 2 , C). Again, see [8] for details. If Y Γ denotes the exterior of the Γ-satellite K Γ ⊂ S 3 of K ⊂ S 3 , then for each JSJ component Y v of Y Γ , we again have reducible and exceptional subsets R v , Z v ⊂ i∈Iv P(H 1 (∂ i Y v ; Z)), along with a lattice Λ v acting on i∈Iv P(H 1 (∂ i Y v ; Z)) by addition of sf v -slopes.
is the exterior of an algebraic-link satellite K Γ ⊂ S 3 of a (possibly trivial) positive L-space knot K ⊂ S 3 , and suppose the triple (p r , q r , n r ) specifies the initial torus-link satellite operation, occurring at the root vertex r ∈ Vert(Γ).
(i.a) If K is nontrivial, qr pr < 2g(K) − 1, p r > 1, and −1 / ∈ j(E in (r)), then This is not as horrible as it looks. Part (i.a) describes the case in which all L-space surgeries yield S 3 . For part (i.b), either we trivially refill all components of Y Γ except for one exterior component in the root, effectively replacing K Γ with K; or, we trivially refill all exterior components but those of Y Γ v(−e) for some incoming edge e, replacing K Γ with some K Γ v(−e) .
The notation Λ Γv and the term 'trivially refill' hide a subtlety, however. For both the above theorem and for Theorem 1.7 for iterated torus-link satellites, we defineΛ Γv to mean While Λ Γv ⊃ u∈Vert(Γv) Λ u , the two sets need not be equal. Similarly, if N > qr pr and , but the containment can be proper. Section 8.2 provides a more explicit characterization of L(Y Γ ) in this case, along with a concrete description of Λ Γ in the case of iterated torus-link satellites.
Part (ii) of Theorem 1.6 is analogous to Theorem 1.2(ii) for torus-link satellites, but this similarity is masked by our transition from S 3 -slopes to sf-slopes. For example, if v is a leaf and its emanating edge e v does not correspond to an exceptional splice, then we have In all other cases, we still have L min + now sits inside the unit-radius neighborhood of R v , with m − v providing a measure of how deeply inside it sits.
at a smoothly spliced leaf v (in part (ii) of the theorem), the notation [·] : Q → Z, [x] := x − x gives the fractional part of a rational number x, whereas the notation [a] b := a − a |b| |b| picks out the smallest nonnegative representative of a mod b for any integers a, b ∈ Z. For a suitable L-space region approximation when q r = 2(K) − 1 and p r = 1, see line (197) and the associated remark.

Iterated torus-link-satellites
For the case of iterated torus-link satellites, we only allow 'smooth splice' edges, corresponding to the original type of torus-link satellite operation. We also drop the algebraicity condition that Δ e > 0, and while we keep all p v , n v > 0 without loss of generality, we allow q v < 0 but demand q v = 0, for each v ∈ Vert(Γ).
is the exterior of an iterated torus-link satellite K Γ ⊂ S 3 of a (possibly trivial) positive L-space knot K ⊂ S 3 , and suppose the triple (p r , q r , n r ) specifies the initial torus-link satellite operation occurring at the root vertex r ∈ Vert(Γ). ( Monotonicity. In both of the above theorems, v∈Vert (Γ) , as discussed in Section 7.6. We say that y Γ or more prosaically (when the above interval interiors are nonempty) is monotone at v if as these are the respective endpoints of the above intervals. The monotone stratumL mono Specifying different collections of local monotonicity conditions allows one to decompose an L-space region into strata of disparate topologies. For example, for the (globally) monotone stratum, we have the following topological result, proved in Section 7.6.
projecting to embedded tori Nonmonotone strata, when they exist, change the topology of the total L-space region and have implications for 'boundedness from below' in the sense of Némethi and Gorsky [13], but we defer the study of nonmonotone regions to later work, whether by this author or others.
New tools. In fact, the propositions in Sections 6 and 7 provide many tools for analyzing questions not addressed in this paper. For example, in the absence of an exceptional splice at v, Proposition 6.2(+)(iii) precisely characterizes when y v(e) 0+ = p * v qv , defining the right-hand boundary of the nonmonotone stratum at that component. These tools can also be used to characterize the nonproduct components of the monotone stratum more explicitly.
New features. Even so, Theorems 1.6 and 1.7 already reveal more interesting behavior than appears for nondegenerate torus-link satellites. In particular, the boundary of the S 3 -slope L-space region need not occur at infinity. For example, if (a) Γ = v specifies a single torus-link satellite of the unknot, and p v = q v = 1; (b) Γ specifies an iterated torus-link satellite, and m + v < 0; or (c) Γ specifies an iterated or algebraic-link satellite, and we restrict to an appropriate piece of L mono sfΓ (Y Γ )| sfv outside the product region, then we encounter regions of the form for −|I v | m + v < 0, with additional components added onto the unit-radius neighborhood of (An analogous phenomenon occurs in the negative direction when m − v > 0.) Thus, in such cases, the L-space region 'wraps around' infinity. In fact, given any n−, n + ∈ Z 0 , it is possible to construct an iterated satellite by torus links for which the S 3 v component of some stratum of the L-space region fills up the quadrant There likewise exist iterated torus-link satellite exteriors Y Γ with u, v ∈ Vert(Γ) for which the projections of L S 3 (Y Γ ) to the positive quadrant < p u q u + 1, +∞ > |Iu| and to the negative We therefore feel that the notion of 'L-space link' should be broadened to encompass any link whose L-space surgery region contains an open neighborhood in the space of slopes, rather than defining this notion in terms of large positive slopes in the L-space surgery region.

Organization
Section 2 establishes basic Seifert fibered space conventions and elaborates on the distinguished slope subsets Λ, R, and Z. Section 3 introduces notation for L-space intervals and proves a new gluing theorem for knot exteriors with graph manifolds. Section 4 introduces machinery developed by the author in [29] to compute L-space intervals for fiber exteriors in graph manifolds, and applies this to prove Theorem 4.5, an sf-slope version of the torus-link satellite results in Theorem 1.2. Section 5 addresses the topology of L-space regions and proves Theorem 1.3. Section 6 describes the graph Γ associated to an iterated torus-link satellite, computes various estimates useful for bounding L-space surgery regions for iterated-toruslink and algebraic link satellites, and proves Theorem 1.7 for iterated-torus-link satellites. Section 7 describes adaptations of this graph Γ to accommodate algebraic link exteriors, discusses monotonicity, and proves Theorems 1.6 and 1.8. Section 8 proves results related to conjectures of Boyer-Gordon-Watson and Juhász, including generalizations of Theorem 1.4.
Readers interested in constructing their own L-space regions for algebraic link satellites or iterated torus-link satellites should refer to the L-space interval technology introduced for graph manifolds in Section 4, and to the analytical tools developed in Section 6.

Basis conventions and the slope subsets Λ, R, and Z
Since all L-spaces are rational homology spheres, any manifold with a positive-genus Seifert fibered JSJ component is necessarily not an L-space. Thus, we shall only ever be interested in genus zero Seifert fibered spaces, and our most important convention is the following one.
Convention 2.1. All Seifert fibered spaces in this paper are of genus zero. Any usage of the term "Seifert fibered" should be taken to mean "genus zero Seifert fibered." is the class of a curve bounding a compressing disk of the solid torus ν(L i ). Any choice of classes λ 1 , . . . , λ n ∈ H 1 (∂Y ; Z) satisfying μ i · λ i = 1 for each i then produces a surgery basis (μ 1 , λ 1 , . . . , μ n , λ n ) for H 1 (∂ i Y ; Z). We call these λ i surgery longitudes, or just longitudes if the context is clear.
When M = S 3 , H 1 (∂Y ; Z) has a conventional basis given by taking each λ i to be the rational longitude; that is, each λ i generates the kernel of the homomorphism ι i * : For M = S 3 , the rational longitude coincides with Seifert-framed longitude.
It is important to keep in mind that for knots and links in S 3 , the conventional homology basis is not always the most natural surgery basis. In particular, any cable or satellite of a knot in S 3 determines a surgery basis for which the surgery longitude corresponds to the Seifert longitude of the associated torus knot or companion knot. This cable surgery basis or satellite surgery basis does not coincide with the conventional basis for S 3 .
For Y a compact oriented 3-manifold with boundary ∂Y = n i=1 ∂ i Y a disjoint union of tori, . . , an bn ), which is the closed 3-manifold given by attaching a compressing disk, for each i, to a simple closed curve in the primitive homology class corresponding to [a i m i + b i l i ] ∈ P(H 1 (∂ i Y ; Z)), and then gluing in a 3-ball to complete this solid torus filling of ∂ i Y . Notationally, we write realizes L(Y (np,nq) ) with respect to the conventional homology basis for link exteriors in S 3

Seifert fibered basis
which makes slopes correspond to Seifert data for Dehn fillings of Y . That is, each −h i is the meridian of the ith excised regular fiber, and eachf i is the lift of the regular fiber class

Action of Λ
The relation i . This choice of global section is not canonical, however. Any new choice of global section would correspond to a new choice of meridians, Writing μ i = β if i − α ih i to express μ i in terms of this new basis yields In other words, the lattice of global section reparameterizations acts on Seifert data, hence on sf-slopes, by addition, without changing the underlying manifold or S 1 fibration. Moreover, for any choice of boundary-homology basis b, the change of basis from sf-slopes to b slopes induces an action of Λ on b-slopes.

Action of Λ on torus-link-exterior slopes
As occurs in the case when Y = Y n (p,q) is the exterior of the torus link T (np, nq) ⊂ S 3 (see (43)), the Λ-action on S 3 -slopes induced by the transformation is of particular interest to us. To aid in the introduction's discussion of the role of Λ in Theorem 1.2, we temporarily introduce the sets L 0 , L 1 , L 2 ⊂ (Q ∪ {∞}) n S 3 of S 3 -slopes, as follows: for some N ∈ Z, where we have temporarily introduced the notation R S 3 to denote the set Finally, for ε > 0, we take U n pq (ε) to be the radius-ε punctured neighborhood of the union of hyperplanes (1) for i = 0 always, for i = 1 when N > pq, and for i = 2 when N pq. (c) For ε > 0, each of the following sets of S 3 -slopes can be realized as a union of finitely many rectangles of dimensions 0, 1, and {n − 1, n}, respectively.
Proof. Part (a). The first statement follows from the fact that 1 We therefore reduce the problem to working withL 0 := L 0 ,L 1 := L 1 , (1). To see this, we first note that since n i=1 l i = 0, l ∈ (Λ sf \ {0}) must have at least one positive and at least one negative component, say and so we conclude that l · ([−∞, pq > n ∪ < pq, +∞] n ) S 3 ⊂ U n pq (1), completing the proof of (b). Part (c). In the sf basis, the complement of U n pq (ε) within the set of S 3 -slopes is given by Since both is a union of finitely many rectangles of dimensions 0, 1, or n in the respective cases that i = 0, i = 1 with N > pq, or i = 2 with N pq. The proof of this latter statement is straightforward, however, since ψ −1 (L i ) is already a finite union of rectangles of dimensions 0, 1, or n, respectively, for the three above respective cases, and only finitely many distinct rectangles can be formed by intersecting Z n translates of these rectangles

Reducible and exceptional sets R and Z
Like the above action of Λ, the following facts about reducible fillings are well known in low-dimensional topology, but for the benefit of a diverse readership we provide some details.
to p − i which winds once positively around D 2 i and winds zero times around the other D 2 j , without intersecting any of the other γ j arcs. Holding the p ± i points fixed while stretching the δ i arcs outward and pulling the γ i arcs tight realizes our global section as the punctured flower shape whereD 2 0 denotes the central disk of the flower, bounded by The Dehn filling Y is formed by multiplying the above global section with the fiber S 1 f and then gluing a solid torus we can decompose the solid torus D 2 f × ∂D 2 0 along the disks D 2 f × p ± i , and distribute these solid-torus components among the boundaries ofD 2 0 and theD 2 i , so that where the union is along the boundary 2-spheres with the connected sum taken along the spheres S 2 i .
This motivates the following terminology. Note that occasionally, slopes in R(Y ) yield Dehn fillings which are connected sums of a lens space with 3-spheres, hence are not reducible.
Definition 2.5. Suppose Y is as above. If the Seifert fibered component containing ∂Y has no exceptional fibers, then the false . Any reducible slopes which are not false reducible are called truly reducible. Equivalently, the truly reducible slopes are those slopes which yield reducible Dehn fillings.

Rational longitudes B
Our last distinguished slope set of interest, the set B of rational longitude slopes, makes sense for Y of any geometric type.
Note that this implies Z = R ∩ B. Moreover, when Y is Seifert fibered, B sf (Y ) is the closure of a linear subspace of sf-slopes. That is, by [28, Section 5] (for example), we have (43), pq , the next proposition follows immediately from line (38).

L-space interval notation
For the following discussion, Y denotes a compact oriented 3-manifold with a onecomponent torus boundary ∂Y , and B is a basis for H 1 (∂Y ; Z), inducing an identification for I (y−,y+) ⊂ P(H 1 (∂Y ; R)) b the closed interval with left-hand endpoint y − and right-hand endpoint y + .
By [28, Proposition 1.3 and Theorem 1.6], the L-space interval L(Y ) ⊂ P(H 1 (∂Y ; Z)) of L-space Dehn filling slopes of Y can only take certain forms.
Proposition 3.2 [28]. One of the following is true.
It is for this reason that we refer to the space of L-space Dehn filling slopes as an interval. It also makes sense to speak of the interior of this interval.
indicates the open interval with left-hand endpoint y − and right-hand endpoint y + . This gives us a new way to characterize the property of Floer simplicity for Y .
• Y has more than one L-space Dehn filling.
In the case that any, and hence all, of these three properties hold, we say that Y is Floer simple.
Both Floer simple manifolds and graph manifolds have predictably behaved unions with respect to the property of being an L-space.
Theorem 3.5 [14,28,29]. If the manifold Y 1 ∪ ϕ Y 2 , with gluing map ϕ : ∂Y 1 → −∂Y 2 , is a closed union of 3-manifolds, each with incompressible single-torus boundary, and with Y i both Floer simple or both graph manifolds, then Unfortunately, this theorem fails to encompass the case in which an L-space knot exterior is glued to a non-Floer simple graph manifold, and our study of surgeries on iterated or algebraic satellites will certainly require this case. We therefore prove the following result.
is a closed union of 3manifolds, such that Y 1 is the exterior of a nontrivial L-space knot K ⊂ S 3 , and Y 2 is a graph manifold, or connected sum thereof, with incompressible single torus boundary, then Moreover, if Y 2 is not Floer simple, then (39) holds for K ⊂ S 3 an arbitrary nontrivial knot.
Proof. We first reduce to the case prime Y 2 . Let Y 2 denote the connected summand of Y 2 containing ∂Y 2 , and recall that hat Heegaard Floer homology tensors over connected sums. Thus, if Y 2 has any non-L-space closed connected summands, then If Y 2 is Floer simple, then when K ⊂ S 3 is an L-space knot, Y 1 is Floer simple, and so the desired result is already given by Theorem 3.5. We therefore assume Y 2 is not Floer simple, In [29], the author showed for any (prime) graph manifold Y 2 with single torus boundary that if F(Y 2 ) (called F d (Y 2 ) in that paper's notation) denotes the set of slopes α ∈ P(H 1 (∂Y 2 ; Z)) for which Y 2 admits a co-oriented taut foliation restricting to a product foliation of slope α On the other hand, Li and Roberts show in [22] that for the exterior of an arbitrary nontrivial knot in S 3 , such as is nonempty. Thus we can construct a co-oriented taut foliation F on Y 1 ∪ ϕ Y 2 by gluing together co-oriented taut foliations restricting to a matching product foliation of some slope α ∈ ϕ P * (F(Y 1 )) ∩ F(Y 2 ) on ∂Y 2 . Eliashberg and Thurston showed in [9] that a C 2 co-oriented taut foliation can be perturbed to a pair of oppositely oriented tight contact structures, each with a symplectic semi-filling with b + 2 > 0. Ozsváth and Szabó [26] showed that one can associate a nonzero class in reduced Heegaard Floer homology to such a contact structure. This result was recently extended to C 0 co-oriented taut foliations by Kazez and Roberts [21] and independently by Bowden [3]. Thus, our co-oriented taut foliation F on Since S 3 is a lens space, any Seifert fibered realization of S 3 can have at most two exceptional fibers: where the right-hand constraint on p, q, p * , q * ∈ Z is necessary (and sufficient) to achieve The above Seifert structure exhibits S 3 as a union where λ −1 and λ 0 are exceptional fibers of meridian- Regular fibers in this Seifert fibration are confined to some neighborhood [−ε, +ε] × T 2 of a torus T 2 , and they foliate this T 2 with fibers all of the same slope. Since λ −1 and λ 0 are of multiplicities p and q, respectively, any regular fiber f wraps p times around the core λ −1 of the solid torus neighborhood ν(λ −1 ), and wraps q times around the core λ 0 of ν(λ 0 ), or equivalently, winds q times along the core of ν(λ −1 ). That is, any regular fiber f is a (p, q) curve in the boundary T 2 = ∂ν(λ −1 ) of the solid torus ∂ν(λ −1 ) of core λ −1 . (See Proposition 4.2 for a more careful treatment of framings and orientations.) Thus, any collection f 1 , . . . , f n of regular fibers in M S 2 (− q * p , p * q ) allows us to realize the exterior of the fiber λ 0 of meridian-slope p * q . This solid-torus link T (np, nq) ⊂Ŷ (p,q) then has exterior To make this association (p, q) →Ŷ n (p,q) well defined, we adopt the following convention.

Construction of satellites
to be the exterior of K (np,nq) ⊂ M .  (47). If the gluing mapφ : on homology, and hence the orientation-preserving linear fractional map (44). The boundary of the compressing disk ofŶ (p,q) is given by the rational longitude l = − • ν(f i ) is the exterior of n regular fibers fromŶ (p,q) = M S 2 (− q * p , * ), we must verify that our liftf 0 ∈ H 1 (∂Ŷ (p,q) ; Z) of a regular fiber class to the boundary ∂Ŷ (p,q) = ∂ 0Ŷ n (p,q) of the solid torusŶ (p,q) is represented by a (p, q) torus knot on ∂Ŷ (p,q) relative to the framing specified by μ and λ. Indeed, from (48), we havẽ as required. The induced mapφ P * on slopes preserves orientation, because the mapφ is orientation reversing, but the surgery basis and Seifert fibered basis are positively oriented and negatively oriented, respectively.

Computing L-space intervals
The primary tool we shall use is a result of the author which computes the L-space interval for the exterior of a regular fiber in a closed 3-manifold with a Seifert fibered JSJ component.
where each Y j is boundary incompressible (that is, is not a solid torus or a connected sum thereof). Write (y 1 , . . . , y n ) for the Seifert slopes ofŶ , so thatŶ is the partial Dehn filling of by (y 1 , . . . , y n ) in our Seifert fibered basis. Further suppose that each Y j is Floer simple, so that we may writē

The above extrema are realized for finite k if and only if Y is boundary incompressible. When
Remarks. In the above, we define y − := ∞ or y + := ∞, respectively, if any infinite terms appear as summands of y − or y + , respectively. For x ∈ R, the notations x and x , respectively, indicate the greatest integer less than or equal to x and the least integer greater than or equal to x, as usual. In addition, we always take k to be an integer. Thus the expression 'k > 0' always indicates k ∈ Z >0 .
In order to use the above theorem, we first have to know whether L(Y ) is nonempty and whether Y is Floer simple. The author provides a complete (and lengthy) answer to this question in [29]. Here, we restrict to the cases of most relevance to the current question.
(i) If n ∞ > 1, then any Dehn filling of Y is a connected sum with S 1 × S 2 , and L sf (Y ) = ∅.
To state the below theorem efficiently, we need to introduce one last notational convention.
Notation. When the brackets [·] are applied to a real number, they always indicate the map Note that the maps · , · , and [·] satisfy the useful identities, We are now ready to classify L-space surgeries on torus-link satellites of L-space knots. which converts the above-specified Seifert basis slopes (Q ∪ {∞}) n sf into conventional link exterior slopes in S 3 , so that L S 3 (Y (np,nq) ) = ψ(L sf (Y (np,nq) )).
(i.a) If N := 2g(K) − 1 > q p , K ⊂ S 3 is nontrivial, and p > 1, then Remarks. A knot K ⊂ S 3 is called a positive (respectively negative) L-space knot if K admits an L-space surgery for some finite S 3 -slope m > 0 (respectively m < 0). Since L S 3 (Y (np,nq) ) = −L S 3 (Ȳ (np,−nq) ) forȲ (np,−nq) , the (np, −nq)-torus-link satellite of the mirror knotK ⊂ S 3 , the above theorem, and Theorem 1.2 are easily adapted to satellites of negative L-space knots or to negative torus links. Any p = 0 satellite is just the n-component unlink, Note that while Theorem 1.2 excludes the case of torus links proper (satellites of the unknot) which are 'degenerate', that is, which have 1 ∈ {p, q}, this case is treated in (iii) above, setting p = 1 without loss of generality. If q = 0 in this case, we again have the n-component unlink. For any nontrivial degenerate torus link, part (iii) above implies that the boundary of L sf follows a piece-wise-constant chaotic pattern, similar to the boundary of the region of Seifert fibered L-spaces. This is unsurprising, since the irreducible surgeries on T (n, n) consist of all oriented Seifert fibered spaces over S 2 of n or fewer exceptional fibers. Finally, if K (np,nq) ⊂ S 3 is any nontrivial-torus-link satellite of a non-L-space knot in S 3 , then the L-space gluing result conjectured in [28] for arbitrary closed oriented 3-manifolds with single-torus boundary -which the authors of [15] have announced they expect to prove in the near future -would imply that L(Y (np,nq) ) = Λ(Y (np,nq) ).
Proof of (ψ). Let Y j := Y (np,nq) sf (0, . . . , 0, ĵ * , 0, . . . , 0) denote the partial Dehn filling of Y (np,nq) which fills in all n boundary components except ∂Y j = ∂ j Y (np,nq) with regular fiber neighborhoods, so that, by the definitions of Y (np,nq) andŶ n (p,q) in (47) and (45), we have withφ as defined in Proposition 4.2, where we recall from Definition 4.1 that pp * − qq * = 1 with 0 q * < p. Observing that Y j has the Dehn filling Y j (−h j ) = S 3 , we take μ j := −h j ∈ H 1 (∂Y j ; Z) for the meridian in our S 3 surgery basis for H 1 (∂Y j ; Z). As shown, for example, in [29], any homology class λ j ∈ H 1 (∂Y j ; Z) representing the rational longitude of Y j has sf-slope π sf (λ j ) given by the negative sum of the sf-slope images of the rational longitudes of the manifolds glued into the boundary components ofŶ n (p,q) , plus the negative sum of Seifert-data slopes (which are just the sf-slope images of the rational longitudes of the corresponding fiber neighborhoods), as follows: This uses the definition in (49) of the induced mapφ P * : P(H 1 (∂Y ; Z)) S 3 → P(H 1 (∂ 0Ŷ n (p,q) Z)) sf on slopes, to calculate the slopeφ P * (π S 3(λ)) =φ P * (π S 3(0)) = p * q ∈ P(H 1 (∂ 0Ŷ n (p,q) Z)) sf . To obtain μ j · λ j = 1, we are constrained by the choice μ j = −h j to select the representative λ j :=f j + pqh j for the sf-slope π sf (λ j ) = − 1 pq . The resulting homology change of basis for H 1 (∂ j Y (np,nq) ; Z) then induces a map on slopes with inverse Setup for (i) and (ii). We begin with the case in which K ⊂ S 3 is nontrivial, so that its exterior Y = S 3 \ • ν(K) is boundary incompressible. It is easy to show (see 'example' in [28,Section 4]) that such Y has L-space interval where Δ(K) and g(K) are the Alexander polynomial and genus of K. Writinḡ we then use (49) to compute that Thus, since y 0+ = q * p , we have For y + , there are multiple cases. Proof of (i): N = 2g(K) − 1 > q p . Since q − Np < 0, we have y 0− < q * p = y 0+ , which, by Theorem 4.4, implies L(Ŷ (np,nq) (y)) = ∅ if and only if y ∈ Q n and y − y + .
Case (a): p > 1. Since 0 < y 0− < q * p < 1, we have so that y − y + if and only if n i=1 ( y i − y i ) 0, which, for y ∈ Q n , occurs if and only if y ∈ Z n . If y ∈ Z n , then y + (k) y + (1) for all k > 0, implying so that Theorem 4.4 tells us Thus, since Y (np,nq) (y) is an L-space if and only if 0 ∈ L sf (Ŷ (np,nq) (y)), we have Case (b): p = 1. In this case, q * p = 0 and y 0− = − 1 N −q , so that In particular, since y which, for y ∈ Q n , occurs only if for some j ∈ {1, . . . , n} we have y i ∈ Z for all i = j. For such a y, we then have For k > 0, set s := k N −q and write k = s(N − q) − t with 0 t < N − q.
Case N < q p . Here, q − Np > 0 implies 0 y 0+ = q * p < y 0− 1. Thus, since 0 ∈< −∞, +∞ >, the n ∞ = 1 case of Theorem 4.4(ii) implies (76) holds, whereas Theorem 4.4(i) implies Z sf (Y (np,nq) ) ⊂ N L sf (Y (np,nq) ). For y ∈ Q n , Theorem 4.4(iii) tells us that L sf (Ŷ (np,nq) (y)) = [[y − , y + ]] with y − y + , so that Y (np,nq) (y) is not an L-space if and only if y + < 0 < y − . We therefore have where the definitions of y − and y + are appropriately adjusted in the case that K ⊂ S 3 is the unknot. Case N < q p with K ⊂ S 3 nontrivial. We already know that y − = − n i=1 y i when K ⊂ S 3 is nontrivial and y ∈ Q n . Thus, it remains to compute y + for y ∈ Q n . Since for all k > 0. Write k = s(q − Np) + t for s, t ∈ Z 0 with s := k q−Np and t < q − Np. Using the facts that (81)), we obtain If n i=1 [−y i ](q − Np) = 0, then, writing k = 1(q − Np) + 0, we can use line (80) to computeȳ + (q − Np), so that we obtain Thus, since (82) implies y + (k) − 1 q−Np − n i=1 y i for all k > 0, we conclude that On the other hand, if Since this bound is realized by y + (1) = − n i=1 y i , we deduce that y + = − n i=1 y i . Thus, since q − Np = p + q − 2g(K)p, the last line of Theorem 4.5(ii) holds.
Case N < q p with p, q > 1 and K ⊂ S 3 the unknot.
we use (49) to compute, forφ P * (L(Y )) sf = [[y 0− , y 0+ ]], that Thus, applying Theorem 4.3 and mildly simplifying, we obtain that y − = sup k>0 y − (k) and y + = inf k>0 y + (k), for (88) For y − (k), we (again) obtain the bound which, for p, q > 1 is realized by To compute y + , we note that since p, q > 1, we can invoke Lemma 4.7 (below), so that (Here, we multiplied the original inequality by k and then observed that the integer on the left-hand side must be bounded by an integer.) In particular, Thus, when a bound which is realized by y + (p + q). We therefore have completing the proof of part (ii).
Proof of (iii): K ⊂ S 3 , p = 1, q > 0. Here, we have the same case as above, but with p = 1 and q > 0, implying q * p = 0 and p * q = 1 q . Thus, the Dehn filling Y (n,nq) sf (y) is the Seifert fibered space M S 2 ( 1 q , y), and we have The above theorem leads to the following Proof. Using the notation we define z(k) ∈ Q for all k ∈ Z >0 , as follows: where we note that This leaves us with the case in which [kq −1 ] p = 1, so that line (98) yields Since [kq −1 ] p = 1 implies k ≡ q (mod p), we can write k = (sq + t)p + q, with s = k−q pq and t ∈ {0 . . . , q − 1}. When t = 0, we obtain On the other hand, when t 1, we have completing the proof of our claim. Since the case k = p + q is subsumed in the case [kq −1 ] p = 1, we also have z(p + q) 0, and so by the induction, it suffices to prove the lemma for k < p + q. Suppose that 0 < k < p + q and k / ∈ pZ (since z(k) 0 for [k] p = 0), so that we now have Since z(aq) = 1 pq (q · a − aq) = 0 for a ∈ Z, we may also assume k / ∈ qZ. Now, the Chinese Remainder Theorem tells us that but since 0 < k < p + q and k / ∈ pZ ∪ qZ, we also have 5. L-space region topology

Topologizing L-space regions
Before examining the topology of various L-space and non-L-space regions, we must first determine a meaningful way to topologize these spaces. We first note that many of the L-space regions we have constructed so far arose as the intersection of the set of rational slopes with a connected space of real slopes. That is not a coincidence. In the Fukaya-category-theoretic description of bordered (Heegaard) Floer homology, as discussed abstractly by Auroux in [1] and realized explicitly in the case of a single torus boundary component by Hanselman, Rasmussen, and Watson in [15], the mechanism that associates a Heegaard Floer group to a choice of Dehn filling slope and spin c structure does not care whether that Dehn filling slope and spin c structure are rational. I do not yet know the correct topological/geometric interpretation for these groups or irrational spin c structures in the case of irrational Dehn fillings, but the groups themselves -along with whether they satisfy the L-space condition -are perfectly well defined.
This has topological consequences for L-space slope regions. Suppose Y is a compact oriented 3-manifold with n-component toroidal boundary , respectively, denote the L-space region and the set of rational longitudes for Y ; that is, B(Y ) is the set of slopes y such that b 1 (Y (y)) > b 1 (Y ) − n. We know that L(Y ) ∩ B(Y ) = ∅ because all L-spaces have b 1 = 0, and we know B(Y ) is closed because it is locally the vanishing locus of the determinant of a matrix. We also know from Proposition 3.2, first proved in [28], that when n = 1, the set L(Y ) ∪ B(Y ) is closed in P(H 1 (∂Y ; Z)).
Our proof of [28, Proposition 3.2] used intrinsically rational methods, but when Hanselman et al. proved the analogous result using Fukaya-category-theoretic bordered Floer homology methods in [15], the closedness of L(Y ) ∪ B(Y ) resulted from a closed condition on the space of real slopes, involving Lagrangian intersections with lines of these slopes. Although an n > 1 version of these Fukaya-category-theoretic methods has not been written down explicitly, from its abstract description I still expect the space L(Y ) ∪ B(Y ) to arise as the intersection of n i=1 P(H 1 (∂ i Y ; Z)) with a space of real slopes cut out by a closed condition. All this is to motivate the idea that the closure ) has intrinsic mathematical meeting and is a natural object of study, hence the following notation.
where ' ' and ' c ', respectively, denote closure and complement in We shall also sometimes use the notation A R for a subset of L(Y ) R deriving from a subset A ⊂ L(Y ) or for a subset of NL(Y ) R deriving from a subset A ⊂ NL(Y ), but in such cases we shall define A R explicitly. We furthermore use the notation [, ] R for closed real intervals.

L-space region topology for torus links
There are five qualitatively different topologies possible for the L-space region of a torus-linksatellite of a knot in S 3 .
Theorem 5.2. For n, p, q ∈ Z with n, p > 0 and gcd(p, q) = 1, let K (np,nq) ⊂ S 3 , with exterior Y (np,nq) :=S 3 \ Remark. The reader may have noticed that in all cases considered in this paper, we have This is a consequence of the general fact that open L-space intervals only ever arise as exteriors of knots in 3-manifolds with S 1 × S 2 connected summands [10]. Note that Z sf ∩ R n sf = ∅.
Thus all of the translates {l + P(N, q)} l∈Λsf are pairwise disjoint, and L R sf deformation retracts onto Λ sf . Proof of (i.b). When 2g(K) − 1 = q p + 1, and n > 1, line (113) still holds, but this time with 1]. To see that |π 0 (L R sf )| = 1, first note that Λ sf is generated by the elements the standard basis element for Z n . Then for any such ε ij and any l ∈ Λ sf , the origin l of the translate P l := l + P (N, q) is path-connected to the origin ε ij + l of the translate P εij +l , via the path γ l ij (t) : Thus L R sf is path connected (hence connected), and in fact, these basic paths γ l ij from l ∈ P l to ε ij + l ∈ P εij +l generate the groupoid G of homotopy classes of paths in L R sf between elements of Λ sf . Let G 0 ⊂ G denote the subset of homotopy classes of paths starting at 0, so that elements of G 0 are uniquely represented by reduced words , where l 0 := 0 and l k+1 : with right-multiplication corresponding to concatenation of paths. Note that since ε ji = −ε ij , we have replaced all instances of γ l ij with (γ l−εji ji ) −1 = γ l ij whenever i > j. If we introduce the free group F ( n 2 ) and epimorphism δ : then an inductive argument on word length shows that the forgetful map on words is invertible. That is, starting with ρ −1 (1) = 1, we can use the inductive rule for any i < j, e ∈ {±1}, and word w ∈< x ij > i<j with known ρ −1 (w), to reconstruct the map ρ −1 . Thus, G 0 inherits the structure of a free group on n 2 generators. Since δ • ρ(g) is the endpoint of any path g ∈ G 0 , we then have Proof of (i.c). When n = 2, the discussion in (i.b) still holds, so |π 0 (L R sf )| = 1 and π 1 (L R sf ) = ker δ = 1. Thus, just as for n = 1, we have L R sf contractible and of dimension 1. Proof of (ii.a). Case N = q p of part (ii) of the proof of Theorem 4.5 states in (77) that where we recall that We therefore have which is contractible and of dimension n. Proof of (ii.b). Since the result is trivial for n = 1, we henceforth assume n > 1. Note that our hypotheses imply q > 0. The statement and proof of Theorem 4.5 then tell us that for all y ∈ Q n sf and for certain c − (k), c + (k) ∈ 1 k Z bounded above and below by linear functions in k, and determined by p, q, and 2g(K) − 1, and on whether K ⊂ S 3 is trivial. In particular, each of c − (k) and c + (k) are independent of y ∈ Q n sf . Since To construct such a deformation retraction, we first define so that for y ∈ Q n sf ,l(y) is the rational longitude of the exteriorŶ (np,nq) (y) := Y (np,nq) (y) \ • ν(f ) of a regular fiber f in Y (np,nq) (y). We then claim that the homotopy provides a deformation retraction from N R to B R sf ∩ R n sf ⊂ N R . First note that (125) also implies that N L sf (Ŷ (np,nq) (z)) =< y + (z), y − (z) > for all z ∈ Q n sf . Thus, for all z ∈ Q n sf , we have l(z) ∈ N L sf (Ŷ (np,nq) (z)), so that l(z) ∈< y + (z), y − (z) >. Thus, for all y ∈ Q n sf , where the equivalence (1 − t)l(y) = l(z t (y)) follows quickly from the definitions of l and z. Whether by Theorem 4.5 or by Calegari and Walker's studies of 'ziggurats' [6], we know that as functions on R n sf , y − and y + are piecewise constant in each coordinate, with rational endpoints. Thus, since l and z are linear and the above inequalities are strict, we have for all y ∈ R n sf and t ∈ [0, 1 > R , where again, [, R and [, ] R denote real intervals. On the other hand, our definitions of y ± and z imply that for any y ∈ N R , we have Combining these three lines of inequalities tells us that for any y ∈ N R , we have z t (y) ∈ N R for all t ∈ [0, 1] R . Thus z provides a deformation retraction from N R to B R sf ∩ R n sf ⊂ N R .

Topology of monotone strata
Sections 6 and 7 analyze the L-space surgery regions for satellites by iterated torus-links and by algebraic links, respectively. While these sections primarily focus on approximation tools, Section 7.6 returns to the question of exact L-space regions for such satellites, and describes how to decompose these L-space regions into strata according to monotonicity criteria, which govern where the endpoints of local L-space intervals lie, relative to asymptotes of maps on slopes induced by gluing maps. Local monotonicity criteria also help determine the topology of these strata, a phenomenon we illustrate with Theorem 7.5 in Section 7, where we show that the B-corrected R-completion of the monotone stratum of the L-space surgery region of an appropriate satellite link admits a deformation retraction onto an embedded torus analogous to that in Theorem 5.2(ii.b) above.

Iterated torus-link satellites
Just as one can construct a torus-link-satellite exterior from a knot exterior by gluing an appropriate Seifert fibered space to the knot exterior (as described in Proposition 4.2), one constructs an iterated torus-link-satellite exterior by gluing an appropriate rooted (tree-)graph manifold to the knot exterior, where this graph manifold is formed by iteratively performing the Seifert-fibered-gluing operations associated to individual torus-link-satellite operations.

Construction of iterated torus-link-satellite exteriors
An iterated torus-link-satellite of a knot exterior Y = M \ • ν(K) is specified by a weighted, rooted tree Γ, corresponding to the minimal JSJ decomposition of the graph manifold glued to the knot exterior to form the satellite. We weight each vertex v ∈ Vert(Γ) by the 3-tuple (p v , q v , n v ) ∈ Z 3 corresponding to the pattern link T v := T (n v p v , n v q v ). As usual, we demand that p v , n v > 0 and that q v = 0. (If any vertex had p v = 0 or q v = 0, then our satellite-link exterior would be a nontrivial connected sum, in which case we might as well have considered the irreducible components of the exterior separately. Moreover, the links of complex surface singularities are irreducible, so the algebraic links we consider later on will necessarily be irreducible.) The weight (p v , q v , n v ) also specifies the JSJ component Y v as the Seifert fibered exterior of T v ⊂Ŷ (pv,qv) as a link in the solid toruŝ for λ −1 the multiplicity-p v fiber of merdional sf-slope y v −1 = − q * v pv , and λ 0 the multiplicity-q v fiber of meridional sf-slope y v 0 = p * v qv , as in Section 4.1. As usual, (p * v , q * v ) ∈ Z 2 denotes the unique pair of integers satisfying Specifying a root r for the tree Γ determines an orientation on edges, up to over-all sign. We choose to direct edges toward the root r, and write E in (v) for the set of edges terminating on a vertex v. On the other hand, each nonroot vertex v has a unique edge emanating from it, and we call this outgoing edge e v . We additionally declare one edge e r to emanate from the the root vertex r toward a null vertex null / ∈ Vert(Γ), which we morally associate (with no hat) to our original knot exterior, For notational convenience, we also associate an 'index' j(e) ∈ {1, . . . , n v(e) } to each edge e, specifying the boundary component is glued when we embed the pattern link T v(−e) in a neighborhood of ∂ j(e) Y v(e) . As such, each edge e ∈ Edge(Γ) corresponds to a gluing map along the incompressible torus joining Y v(−e) to Y v(e) . This ϕ e is the inverse of the mapφ used in the satellite construction of Proposition 4.2. We express its induced map on slopes in terms of sf-slopes on both sides. Thus ϕ P e * is orientation reversing. Note that for any v ∈ Vert(Γ), the map ϕ P ev * is determined by (p v , q v , n v ) and j(e v ). We additionally define for each v ∈ Vert(Γ), so that the space of Dehn filling slopes of Y Γ is given by Writing Γ v for the subtree of Γ of which v is the root, let Y Γv denote the graph manifold with JSJ decomposition given by the Seifert fibered spaces Y u and gluing maps ϕ e(u) for u ∈ Vert(Γ v ), so that Y Γv is constructed recursively as The exterior

Dehn fillings of Y Γ
For v ∈ Vert(Γ), any sf Γv -slope determines an L-space interval L(Y Γv (y Γv )) for the sf Γv -Dehn-filling Y Γv (y Γv ). If Y Γv (y Γv ) is Floer simple, then we write to express L sfv (Y Γv (y Γv )) in terms of sf v -slopes and sf v(ev) -slopes, respectively. Note that since ϕ P ev * is orientation-reversing, we have If we focus instead on the incoming edges of v, then any Dehn filling of the boundary components ∂Y Γv \ ∂Y v of Y Γv allows us to partition the graph manifolds incident to v, labeled by J v = {j(e)|e ∈ E in (v)}, according to whether they are boundary compressible (bc) -a solid torus or connected sum thereof -or boundary incompressible (bi): Recalling that Theorem 4.3 implies y v j− = y v j+ for any j ∈ J bc v , we set y v j := y v j± for all j ∈ J bc v . We additionally define the sets J bi+ vZ , J bi− vZ and J bc vZ : For

and otherwise set
In addition, defineȳ v The 'sup' and 'inf' account for cases in whichȳ v 0± (k) = 0. The above notation provides a convenient way to repackage our computation of L-space interval endpoints.
) sfv are the (potential) L-space interval endpoints for Y Γv (y Γv ) as defined in Theorem 4.3, then Proof. The displayed equations in Proposition 6.1 come directly from the definitions of y v 0± specified by Theorem 4.3, but subjected to some mild manipulation of terms using the facts that x = x + [x] and x = x − [−x] for all x ∈ R, and that For the second half of the proposition, first note that theȳ v 0∓ = q * v pv result follows directly from taking the k → ∞ limit. In the case of ∞ / for all k ∈ Z >0 . If J bi+ vZ = ∅ (respectively, J bi− vZ = ∅), then the above bound forŷ v 0− (k) (respectively,ŷ v 0+ (k)) is nonincreasing (respectively, nondecreasing) in k, so that for all k ∈ Z >0 . Since these bounds are each realized when k = 1, this completes the proof of the bottom line of the proposition.
The above method of computation for L-space interval endpoints helps us to prove some useful bounds for these endpoints.
where we note that for a, b ∈ Z with a, b < qv pv , one has To aid in the proof of (=), we first prove the following Claim. If the hypotheses of Proposition 6.2 hold, then Proof of Claim. For the ⇒ direction, the left-hand side implies the irreducible component of Y Γv (y Γv ) containing ∂Y Γv (y Γv ) is Seifert fibered over the disk with one or fewer exceptional fibers, hence is bc, and direct computation shows pv . For the ⇐ direction, suppose the right-hand side holds. Then J bi v = ∅, and the irreducible component of Y Γv (y Γv ) containing ∂Y Γv (y Γv ) is Seifert fibered over the disk with one or fewer exceptional fibers, implying |{ Proof of (−) and part of (=). When J bi+ vZ = ∅, (−) follows from Proposition 6.1, which tells pv . The latter case implies sup k→+∞ȳ v 0− (k) is not attained for finite k, and so Theorem 4.3 tells us that Proof of (+) and remainder of (=). Proposition 6.1 tells us thatȳ v 0+ = 1 when J bi− vZ = ∅, so we henceforth assume J bi− vZ = ∅. In this case, we havē for all k ∈ Z >0 , and soȳ v This leaves us with (+.iii). Since q v > p v > 1 implies p * v qv < 1, but Proposition 6.1 tells us Setting m = 0 in (+.i) then gives us Similarly, setting m = −1 in (+.i) yields the relation where we used (+.ii) for the right-hand inequality. Finally, supposeȳ v 0+Σ (q v + p v ) > 0. By reasoning similar to that used in the proof of (+.i), this implies thatȳ v 0+Σ (k) k pv+qv for all k ∈ Z >0 . We then havē with the right-hand inequality coming from Lemma 4.7, and soȳ v making the right-hand side of (169) negative.
We therefore henceforth assume that Proof of (ii). The claim holds vacuously for [−p v ] qv ∈ {0, 1}, so we assume [−p v ] qv 2 and q v −3, in which case Sinceȳ Using arguments similar to those in part (i), it is straightforward to derive the bound for all k ∈ Z >0 , and to show that the right-hand side is negative if and since Proofs of (iii) and (iv). Respectively similar to proofs of (ii) and (i).
6.3. L-space surgery regions for iterated satellites: Proof of Theorem 1.7 We have finally done enough preparation to prove Theorem 1.7 from the introduction.
Proof of Theorem 1.7. The bulk of part (i) is proven in the Claim in the proof of Theorem 8.1. Since the right-hand condition of (265) is equivalent to the condition that Y Γ (y Γ ) be an L-space, the Claim proves that Y Γ (y Γ ) is an L-space if and only if Y Γ (y Γ ) = S 3 . Thus, if we define Λ Γ as in (11), then the statement L(Y Γ ) = Λ Γ holds tautologically.
The proof of part (ii) begins similarly to the proof of Theorem 4.5(i.b), except that instead of deducing that i∈Ir ( y r i − y r i ) 1, we deduce that with y r j− y r j+ for all j ∈ J bc r . In the case that i∈Ir ( y r i − y r i ) = 1 and the other sums vanish, we are reduced to the original case of Theorem 4.5(i.b), obtaining the component In the case that i∈Ir ( y r i − y r i ) = 0, we have that y r ∈ Z |Ir| , and all but one incoming edge of r, say e, descend from trees with trivial fillings. Performing these trivial fillings reduces Y Γ to the exterior of a Γ v(−e) -satellite of the (1, q r )-cable of K ⊂ S 3 , but the (1, q r )-cable is just the identity operation, so we are left with the exterior Y Γ v(−e) of the Γ v(−e) -satellite of K ⊂ S 3 . Considering this for all edges e ∈ E in (r) then gives the remaining component Part (iii). Before proceeding with the main inductive argument in this section, we attend to some bookkeeping issues. In particular, our inductive proof requires each I v to be nonempty. For any w ∈ Vert(Γ) with I w = ∅, we repair this situation artificially, as follows. First, redefine where, again, y v j(e)± := ϕ P e * (y v(−e) 0∓ ]]. Note that this inductive assumption already holds vacuously if v is a leaf. If If y v ∈ L min − sfv ∪ L min + sfv ⊂ Q |Iv| , then applying (182) to Proposition 6.1 yields and assuming (182) for Theorem 4.4 implies Suppose y v ∈ L min + sfv , so that the bound i∈Iv y v i m + v , together with (185), implies Since ϕ P ev * is locally monotonically decreasing in the complement of its vertical asymptote at where φ P ev * (∞) = pv qv is the location of the horizontal asymptote of ϕ P ev * . Thus, since pv qv − 1 < pv qv = φ P ev * (∞), we deduce that to finish establishing our inductive hypotheses for e v in the y v ∈ L min + sfv case, it suffices to show that If |q v | = 1, it is straightforward to compute that (188) and (192) that (191) holds. Next suppose that |q v | > 1, so that If 0 < pv qv < 1, this makes (ϕ P ev * ) −1 ( pv qv − 1) = q * v pv , so that (191) follows from (188) and the fact thatȳ 0− q * v pv , with equality only if Y Γv (y Γv ) is boundary compressible. This leaves the cases in which pv qv > 1 or , and so (191) follows from part (i) or (ii), respectively, of Proposition 6.3.
completing our inductive step for the case of y v ∈ L min + sfv . The proof of our inductive step for the case of y v ∈ L min − sfv follows from symmetry under orientation reversal.
Recall that we regard the root vertex r at the bottom of the tree Γ = Γ r as having an outgoing edge e r pointing to the empty vertex v(e r ) := null, where this null vertex v(e r ) corresponds to the exterior Y := S 3 \ • ν(K) of the companion knot K ⊂ S 3 , from which the satellite exterior Y Γ := Y Γ ∪ Y is formed. Recursing down to this null vertex v(e r ), our above induction shows that for any y Γ ∈ v∈Vert(Γr) ( implying y v(er) j(er)− < 1 N , and thereby completing the proof of the theorem.
Remark. It is only in (196) that we use the hypothesis of part (iii) that q r > 2g(K) − 1 =: N . In the case that we do have p r = 1 and q r = N , this implies (ϕ P er * ) −1 ( 1 N ) = ∞, requiring L min − sfr to be empty, but we still have the modified result that (197)

Smooth and exceptional splices
As mentioned in the introduction, the class of algbraic link satellites is slightly more general than the class of iterated torus link satellites, in that the JSJ decomposition graph of the exterior must allow one extra type of edge.
To describe how this new type of edge is different, we first address the notion of splice maps. Suppose K 1 ⊂ M 1 and K 2 ⊂ M 2 are knots in compact oriented 3-manifolds M 1 and M 2 , with each ∂M i a possibly-empty disjoint union of tori.
for each exterior, with λ i the Seifert longitude if M i is either an integer homology sphere or a link exterior in a specified integer homology sphere.
A gluing map φ : ∂ 0 Y 1 → −∂ 0 Y 2 is then called a splice if the induced map on homology sends μ 1 → λ 2 and μ 2 → λ 1 . Gluings via splice maps are minimally disruptive to homology. For instance, if M 2 is an integer homology sphere, then is the exterior of the satellite link of the companion knot K 1 ⊂ M 1 by the pattern link L 2 ⊂ (S 3 \ • ν(K 2 )). For satellites by T (np, nq), this unknot K 2 ⊂ M 2 is the multiplicity-q fiber λ 0 ⊂ Y n (p,q) in the T (np, nq)-exterior In an iterated torus-link satellite, we only perform satellites on components of the companion link we are building. That is, for an edge e ∈ Edge(Γ) from v(−e) to v(e), we always form a T v(e) -torus-link satellite that splices the multiplicity-q v(−e) -fiber λ v(−e) 0 , with exterior

Slope maps induced by splices
For the induced maps on slopes, we have for an edge e corresponding to a smooth splice, and for an edge e corresponding to an exceptional splice. To accommodate our notation to these two different types of maps, we define φ e := σ e j(e) = −1 ϕ e j(e) = −1.
In addition, since the exceptional fiber at ∂ −1 Y v is only exceptional if p v > 1, we adopt the convention that exceptional splice edges only terminate on vertices v with p v > 1.

Algebraic links
Eisenbud and Neumann show in [8] that a graph Γ with such edges and vertices specifies an algebraic link exterior if and only if Γ satisfies the algebraicity conditions Δ e > 0 for all e ∈ Edge(Γ), j(e) = −1 .
ensuring negative definiteness. Eisenbud and Neumann also prove that any algebraic link exterior can be realized by such a graph. Note that the above algebraicity conditions imply For notational convenience, we adopt the convention that J v remains the same, only indexing incoming edges corresponding to smooth splices. That is, we define and its complement I v still indexes the remaining boundary components, Finally, since φ e is always orientation-reversing, the induced map φ P e * is still decreasing with respect to the circular order on sf-slopes, and the impact of φ P e * on the linear order of finite sf-slopes still depends on the positions of the horizontal and vertical asymptotes respectively, of the graph of φ P e * . More explicitly, we have , respectively. We perform such modifications as follows. First, for v ∈ Vert(Γ), with Γ specifying an algebraic link exterior, set and for k ∈ Z >0 , define y v −1+ (k) and y v −1− (k) by setting where again, e ∈ E in (v) is the unique incoming edge with j(e ) = −1, if such e exists. If −1 / ∈ j(E in (v)), then we take Y Γ v(−e ) (y Γ v(−e ) ) to be boundary-compressible.
Next, we defineȳ v 0− (k) andȳ v 0+ (k) to be respective results of replacing the summand (151), and replacing the summand (152). That is, we set and by analogy with the definition ofȳ v 0± in (209), we definē We are now ready to state and prove an analog of Proposition 6.1 and a supplement to Proposition 6.2.
Proof of Theorem 1.6. The proofs of parts (i and (ii) are the same as those in the iterated torus link satellite case, if one keeps in mind that the p r = 1 condition for (ii.b) and an explicit hypothesis for (ii.a) each rule out the possibility of an incoming exceptional splice at the root vertex.
The proof of part (iii) also adapts the proof used for iterated torus satellites, but we provide more details in this case. Again, for bookkeeping convenience, we redefine I w := {1} and set L min + sfw := {0} and R sfw \ Z sfw := L min − sfw := ∅, for any w ∈ Vert(Γ) with I w = ∅. For a vertex v ∈ Vert(Γ), we inductively assume, for each incoming edge e ∈ E in (v), that for any y Γ v(−e) ∈ u∈Vert(Γ v(−e) ) (L min + sfu ∪ R sfu \ Z sfu ∪ L min − sfu ), we have where μ e := φ P The statement of Theorem 1.6 makes the substitution q v(−e) + 1 → 1 for the j(e) = −1 case of m e− , in its role as a summand of of m − v . However, this substitution is an equivalence for all v ∈ Vert(Γ) and e ∈ E in (v), since the algebraicity condition (203) implies 0 < q v(−e) < 1 for j(e) = −1. Note that this does not imply 0 < pr qr < 1 for the root vertex r = v(−e r ), because of our declared convention that v(e r ) = null / ∈ Vert(Γ). The algebraicity condition (203) also implies that the conditions q = +1, q < 0, and pv qv > +1 are never met for j(e v ) = −1 and v = r. Thus, the j(e) = −1 cases of our definitions of L min − sfv and L min + We assume y v ∈ L min − sfv ∪ L min + sfv for the remainder. This assumption, together with our inductive assumptions, makes Theorem 4.4 yield and Proposition 6.2 tells us We furthermore already know thatȳ v 0± =ȳ v 0± when −1 / ∈ j(E in (v)). Combining this fact with Proposition 7.2, given our inductive assumptions, yields Suppose y v ∈ L min + sfv . Then from Proposition 7.1, we have Thus, altogether we have Here, η v := (φ P ev * ) −1 (∞) is the location of the vertical asymptote of φ P ev * . The inequality q * v pv < η v follows directly from the computation of η in (208), plus the fact that qv . Since φ P ev * is locally monotonically decreasing on the complement of η v , this implies that all the expressions on the left-hand side of (233) have φ P ev * -images below the horizontal asymptote at ξ v(ev) , but in reverse order. That is, we have Thus, since m ev+ = 0 and since (226) shows that ξ v(ev) < μ ev + m ev− , we obtain with equality only if Y Γv (y Γv ) is bc. Finally, suppose y v ∈ L min − sfv . Then combining Proposition 7.1 (for line (236)) with the righthand inequality of (229), the inductive upper bounds on y v j for j ∈ J v := j(E in (v))| >0 , and the upper bound i∈Iv y v i m − v for y v ∈ L min − sfv (for line (237)), we obtain j(e)− , as a function of y Γ | Γ v(−e) , for each edge e ∈ Edge(Γ) and slope y Γ ∈ L min sfΓ (Y Γ ). This implies that L min sfΓ (Y Γ ) is confined to a particular substratum of L sfΓ (Y Γ ), called the monotone stratum.
The monotone stratum L mono sfΓ (Y Γ ) of L sfΓ (Y Γ ) is then the set of slopes y Γ ∈ L sfΓ (Y Γ ) such that y Γ is monotone at all v ∈ Vert(Γ).
In the above, for brevity, we have adopted the following corresponding to the endpoint-ordering consistent with that for generic Seifert fibered Lspace intervals. We call this condition 'monotonicity' because of its preservation of this ordering.
The tools developed in Sections 6 and 7 can be used in much more general settings than that of the inner approximation theorems we proved, so long as one first decomposes L sfΓ (Y Γ ) into strata according to monotonicity conditions, similar to how torus link satellites must first be classified according to whether 2g(K) − 1 q p . Monotonicity conditions also impact the topology of strata.
Theorem 7.5. Suppose that K Γ ⊂ S 3 is an algebraic link satellite, specified by Γ, of a positive L-space knot K ⊂ S 3 , where either K is trivial, or K is nontrivial with qr pr > 2g(K) − 1. Let V ⊂ Vert(Γ) denote the subset of vertices v ∈ V for which |I v | > 0.
Then the B sfΓ -corrected R-completed monotone stratum L mono sfΓ (Y Γ ) R := L mono sfΓ (Y Γ ) \ B sfΓ is of dimension |I Γ | and deformation retracts onto an (|I Γ | − |V |)-dimensional embedded torus, Proof. We argue by induction, recursing downward from the leaves of Γ towards its root. Observe that for any v ∈ Vert(Γ), we have the fibration  (208), is the position of the vertical asymptote of φ P ev * ), along with a few minor analogous adjustments corresponding to this change.
It remains to show that the fibration in (248) is trivial, but this follows from the fact that

Extensions of L-space Conjecture Results
As mentioned in the introduction, Boyer-Gordon-Watson [5] conjectured several years ago that among prime, closed, oriented 3-manifolds, L-spaces are those 3-manifolds whose fundamental groups do not admit a left orders (LO). Similarly, Juhász [20] conjectured that prime, closed, oriented 3-manifold are L-spaces if and only if they fail to admit a co-oriented taut foliation (CTF). Procedures which generate new collections of L-spaces or non-L-spaces, such as surgeries on satellites, provide new testing grounds for these conjectures.
For Y a compact oriented 3-manifold with boundary a disjoint union of n > 0 tori, define the slope subsets F(Y ), Y admits a CTF F such that F| ∂Y is the product foliation of slope α. , Note that α ∈ F(Y ) implies that Y (α) admits a CTF, but the converse, while true for Y a graph manifold, is not known in general.

Proof of Theorem 1.4 and Generalizations
The proof of Theorem 1.4 relies on the related gluing behavior of co-oriented taut foliations, left orders on fundamental groups, and the property of being an non-L-space, for a pair Y 1 , Y 2 of compact oriented 3-manifolds with torus boundary glued together via a gluing map ϕ : ∂Y 1 → ∂Y 2 . That is, the contrapositives of Theorems 3.5 and 3.6 tell us that if Y i have incompressible boundaries and are both Floer simple manifolds, both graph manifolds, or an L-space knot exterior and a graph manifold, then The analogous statements for CTFs and LOs, while true for graph manifolds (once an exception is made for reducible slopes in the case of CTFs), are not established in general. However, we still have weak gluing statements in the general case. Since product foliations of matching slope can always be glued together, we have Moreover, Clay, Lidman, and Watson [7] built on a result of Bludov and Glass [2] to show that