The nearby Lagrangian conjecture for pinwheels
Pith reviewed 2026-05-25 02:42 UTC · model grok-4.3
The pith
Any two embeddings of Lagrangian (p,q)-pinwheels in the rational homology ball B_{p,q} are related by compactly supported Hamiltonian isotopy.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
Any two embeddings of Lagrangian (p,q)-pinwheels in B_{p,q} are related by a compactly supported Hamiltonian isotopy, establishing the nearby Lagrangian conjecture for this wide class of singular Lagrangians.
What carries the argument
The pintwist τ_{p,q}, the generator of the compactly supported symplectomorphism group Symp_c(B_{p,q}).
If this is right
- Gromov non-squeezing holds for pin-balls.
- The local Lagrangian unknotting theorem of Eliashberg--Polterovich receives a new proof.
- The only Lagrangian (n,m)-pinwheel that embeds in B_{p,q} is the one of type (p,q).
Where Pith is reading between the lines
- The neck-stretching and blow-up techniques may apply to uniqueness questions for other singular Lagrangian skeletons in rational homology balls.
- The generation result for Symp_c suggests that similar twist generators could control isotopy classes in related 4-dimensional symplectic manifolds.
- The result constrains possible Lagrangian pinwheels in fillings of contact manifolds with the same boundary as B_{p,q}.
Load-bearing premise
The compactly supported symplectomorphism group of B_{p,q} is generated by the pintwist τ_{p,q}.
What would settle it
An explicit pair of (p,q)-pinwheel embeddings in B_{p,q} that cannot be connected by any compactly supported Hamiltonian isotopy.
Figures
read the original abstract
The Lagrangian skeleton of the rational homology ball $B_{p,q}$, for $0<q<p$ coprime integers, is an immersed but not embedded Lagrangian, called a $(p,q)$-pinwheel. We show that any two embeddings of Lagrangian $(p,q)$-pinwheels in $B_{p,q}$ are related by a compactly supported Hamiltonian isotopy, establishing Arnold's nearby Lagrangian conjecture for this wide class of singular Lagrangians. Our proof has two largely independent parts: the first uses neck-stretching and the symplectic rational blow-up to understand embeddings of pinwheels up to symplectomorphism; the second computes that $\text{Symp}_c(B_{p,q})$ is generated by a twist about the pinwheel, which we call the pintwist $\tau_{p,q}$. We provide three applications of our methods: Gromov non-squeezing for pin-balls; a new proof of the local Lagrangian unknotting theorem of Eliashberg--Polterovich; and that the only Lagrangian $(n,m)$-pinwheel in $B_{p,q}$ is of type $(p,q)$.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proves Arnold's nearby Lagrangian conjecture for (p,q)-pinwheels (0<q<p coprime) in the rational homology ball B_{p,q}: any two Lagrangian embeddings of such pinwheels are related by a compactly supported Hamiltonian isotopy. The argument splits into two largely independent parts: (i) neck-stretching combined with symplectic rational blow-up to classify embeddings up to symplectomorphism, and (ii) an explicit computation showing that Symp_c(B_{p,q}) is generated by the single element τ_{p,q} (the pintwist). Three applications are derived: Gromov non-squeezing for pin-balls, a new proof of the Eliashberg–Polterovich local Lagrangian unknotting theorem, and uniqueness of the (p,q)-type among (n,m)-pinwheels in B_{p,q}.
Significance. If the two parts hold, the result is a notable advance in symplectic geometry: it settles the nearby Lagrangian conjecture for a broad family of singular (immersed but not embedded) Lagrangians and supplies concrete applications that recycle the same techniques. The explicit group-generation computation and the separation of the classification step from the isotopy step are strengths; both reduce the scope for hidden assumptions. The work also supplies a new proof of an existing theorem, which is useful for the literature.
minor comments (3)
- [Introduction] The abstract states that the two parts are 'largely independent,' but the introduction should contain a short paragraph (perhaps after the statement of the main theorem) explaining why the classification up to symplectomorphism does not feed into the group-generation computation and vice versa.
- [§3 (neck-stretching section)] Notation for the rational blow-up and the almost-complex structures used in the neck-stretching limit should be introduced once, with a single consistent symbol, rather than redefined in each subsection.
- [Applications] The three applications are stated only in the abstract and introduction; a dedicated short section or subsection collecting the statements and indicating which parts of the main argument are reused would improve readability.
Simulated Author's Rebuttal
We thank the referee for their positive summary, significance assessment, and recommendation of minor revision. No specific major comments were raised in the report.
Circularity Check
No significant circularity identified
full rationale
The paper's proof is structured as two explicitly independent parts: (1) classification of pinwheel embeddings up to symplectomorphism via neck-stretching and rational blow-up, and (2) direct computation that Symp_c(B_{p,q}) is generated by the pintwist τ_{p,q}. The central claim (nearby Lagrangian conjecture for these pinwheels) is the conjunction of these parts. No load-bearing step reduces by definition, fitted input, or self-citation chain to its own outputs; the second part is presented as an explicit group computation rather than an appeal to prior results by the same authors. The derivation is therefore self-contained against external benchmarks with no circular reduction visible from the given structure.
Axiom & Free-Parameter Ledger
axioms (1)
- standard math Standard properties of symplectic manifolds, Lagrangian submanifolds, and Hamiltonian isotopies
Reference graph
Works this paper leans on
-
[1]
Nearby Lagrangians with vanishing Maslov class are homotopy equivalent
M. Abouzaid. “Nearby Lagrangians with vanishing Maslov class are homotopy equivalent”. In:Invent. Math.189.2 (2012), pp. 251–313.doi:10.1007/s00222-011-0365-0
-
[2]
M. Abouzaid, D. ´Alvarez-Gavela, S. Courte, and T. Kragh.Normal invariant of nearby Lagrangians via twisted derivative. 2025. arXiv:2505.12515 [math.SG]
-
[3]
Twisted generating functions and the nearby Lagrangian conjecture
M. Abouzaid, S. Courte, S. Guillermou, and T. Kragh. “Twisted generating functions and the nearby Lagrangian conjecture”. In:Duke Math. J.174.5 (2025), pp. 949–1011.doi:10. 1215/00127094-2024-0052
work page 2025
-
[4]
Simple homotopy equivalence of nearby Lagrangians
M. Abouzaid and T. Kragh. “Simple homotopy equivalence of nearby Lagrangians”. In:Acta Math.220.2 (2018), pp. 207–237.doi:10.4310/ACTA.2018.v220.n2.a1
-
[5]
Topology of symplectomorphism groups ofS 2 ×S 2
M. Abreu. “Topology of symplectomorphism groups ofS 2 ×S 2”. In:Invent. Math.131.1 (1998), pp. 1–23.doi:10.1007/s002220050196
-
[6]
Topology of symplectomorphism groups of rational ruled sur- faces
M. Abreu and D. McDuff. “Topology of symplectomorphism groups of rational ruled sur- faces”. In:J. Am. Math. Soc.13.4 (2000), pp. 971–1009.doi:10.1090/S0894- 0347- 00- 00344-1
-
[7]
Embeddings and disjunction of Lagrangian pinwheels via rational blow-ups
N. Adaloglou. “Embeddings and disjunction of Lagrangian pinwheels via rational blow-ups”. In:J. Symplectic Geom.24.1 (2026), pp. 105–129.doi:10.4310/JSG.260423234950
-
[8]
Uniqueness of Lagrangians inT ∗RP 2
N. Adaloglou. “Uniqueness of Lagrangians inT ∗RP 2”. In:Ann. Math. Qu´ e.49.1 (2025), pp. 215–222.doi:10.1007/s40316-024-00238-3
-
[9]
N. Adaloglou, J. Brendel, J. Evans, J. Hauber, and F. Schlenk.Markov staircases. 2025. arXiv:2509.03224 [math.SG]
-
[10]
N. Adaloglou and J. Hauber.Pinwheels in symplectic rational and ruled surfaces and non- squeezing of rational homology balls. 2025. arXiv:2503.16250 [math.SG]. REFERENCES 65
-
[11]
Symplectic staircases for domains in cotangent bundles
N. Adaloglou and J. Hauber. “Symplectic staircases for domains in cotangent bundles”. Forthcoming
-
[12]
M. Atallah, C. Y. Mak, and W. Wu.C 0-rigidity of the Hamiltonian diffeomorphism group of symplectic rational surfaces. Preprint, arXiv:2508.20285 [math.SG]. 2025
-
[13]
Lagrangian skeletons, periodic geodesic flows and symplectic cuttings
M. Audin. “Lagrangian skeletons, periodic geodesic flows and symplectic cuttings”. In: Manuscr. Math.124.4 (2007), pp. 533–550.doi:10.1007/s00229-007-0134-y
-
[14]
Asymptotically holomorphic families of symplectic submanifolds
D. Auroux. “Asymptotically holomorphic families of symplectic submanifolds”. In:Geom. Funct. Anal.7.6 (1997), pp. 971–995.doi:10.1007/s000390050033
-
[15]
Sur la structure du groupe des diff´ eomorphismes qui preservent une forme symplectique
A. Banyaga. “Sur la structure du groupe des diff´ eomorphismes qui preservent une forme symplectique”. In:Comment. Math. Helv.53 (1978), pp. 174–227.doi:10.1007/BF02566074
-
[16]
Symplectic fillings of links of quotient surface singularities
M. Bhupal and K. Ono. “Symplectic fillings of links of quotient surface singularities”. In: Nagoya Math. J.207 (2012), pp. 1–45
work page 2012
-
[17]
Spherical Lagrangians via ball packings and symplectic cutting
M. S. Borman, T.-J. Li, and W. Wu. “Spherical Lagrangians via ball packings and symplectic cutting”. In:Sel. Math., New Ser.20.1 (2014), pp. 261–283.doi:10.1007/s00029- 013- 0120-z
-
[18]
Compactness results in symplectic field theory
F. Bourgeois, Y. Eliashberg, H. Hofer, K. Wysocki, and E. Zehnder. “Compactness results in symplectic field theory”. In:Geom. Topol.7 (2003), pp. 799–888.doi:10.2140/gt.2003. 7.799
-
[19]
Pinwheels as Lagrangian barriers
J. Brendel and F. Schlenk. “Pinwheels as Lagrangian barriers”. In:Commun. Contemp. Math. 26.5 (2024). Id/No 2350020, p. 21.doi:10.1142/S0219199723500207
-
[20]
M. R. Buck.Lagrangian Spheres and Cyclic Quotient T-singularities. 2025. arXiv:2509 . 18976 [math.SG]
work page 2025
-
[21]
Compactness for punctured holomorphic curves
K. Cieliebak and K. Mohnke. “Compactness for punctured holomorphic curves”. In:J. Sym- plectic Geom.3.4 (2005), pp. 589–654.doi:10.4310/JSG.2005.v3.n4.a5
-
[22]
D. Cristofaro-Gardiner, N. Magill, and D. McDuff.Curvy points, the perimeter, and the complexity of convex toric domains. Preprint, arXiv:2506.23498 [math.SG]. 2025
-
[23]
The classification of Lagrangians nearby the Whitney immersion
G. Dimitroglou Rizell. “The classification of Lagrangians nearby the Whitney immersion”. In:Geometry & Topology23 (2019), pp. 3367–3458.doi:10.2140/gt.2019.23.3367
-
[24]
Lagrangian isotopy of tori inS 2 ×S 2 andCP 2
G. Dimitroglou Rizell, E. Goodman, and A. Ivrii. “Lagrangian isotopy of tori inS 2 ×S 2 andCP 2”. In:Geom. Funct. Anal.26.5 (2016), pp. 1297–1358.doi:10.1007/s00039-016- 0388-1
-
[25]
Introduction to Symplectic Field Theory
Y. Eliashberg, A. Givental, and H. Hofer. “Introduction to Symplectic Field Theory”. In: GAFA 2000. Visions in mathematics—Towards 2000. Proceedings of a meeting, Tel Aviv, Israel, August 25–September 3, 1999. Part II.Basel: Birkh¨ auser, 2000, pp. 560–673
work page 2000
-
[26]
Local Lagrangian 2-knots are trivial
Y. Eliashberg and L. Polterovich. “Local Lagrangian 2-knots are trivial”. In:Ann. Math. (2) 144.1 (1996), pp. 61–76.doi:10.2307/2118583
- [27]
-
[28]
Evans.KIAS Lectures on Symplectic Aspects of Degenerations
J. Evans.KIAS Lectures on Symplectic Aspects of Degenerations. Preprint, arXiv:2403.03519 [math.SG]. 2024. 66 REFERENCES
-
[29]
Evans.Lectures on Lagrangian Torus Fibrations
J. Evans.Lectures on Lagrangian Torus Fibrations. London Mathematical Society Student Texts. Cambridge University Press, 2023.doi:10.1017/9781009372671
-
[30]
Symplectic mapping class groups of some Stein and rational surfaces
J. Evans. “Symplectic mapping class groups of some Stein and rational surfaces”. In:J. Symplectic Geom.9.1 (2011), pp. 45–82.doi:10.4310/JSG.2011.v9.n1.a4
-
[31]
Bounds on Wahl singularities from symplectic topology
J. Evans and I. Smith. “Bounds on Wahl singularities from symplectic topology”. In:Algebr. Geom.7.1 (2020), pp. 59–85.doi:10.14231/AG-2020-003
-
[32]
Markov numbers and Lagrangian cell complexes in the complex projective plane
J. Evans and I. Smith. “Markov numbers and Lagrangian cell complexes in the complex projective plane”. In:Geom. Topol.22.2 (2018), pp. 1143–1180.doi:10.2140/gt.2018.22. 1143
-
[33]
Infinitely many exotic monotone Lagrangian tori inCP 2
R. Ferreira de Velloso Vianna. “Infinitely many exotic monotone Lagrangian tori inCP 2”. In:J. Topol.9.2 (2016), pp. 535–551.doi:10.1112/jtopol/jtw002
-
[34]
Exact Lagrangian submanifolds in simply-connected cotangent bundles
K. Fukaya, P. Seidel, and I. Smith. “Exact Lagrangian submanifolds in simply-connected cotangent bundles”. In:Invent. Math.172.1 (2008), pp. 1–27.doi:10.1007/s00222-007- 0092-8
-
[35]
M. Golla and B. Owens.The Farey tree and embeddings of lens spaces and rational balls in CP2. Preprint, arXiv:2512.09183 [math.GT]. 2025
-
[36]
Locality of relative symplectic cohomology for com- plete embeddings
Y. Groman and U. Varolgunes. “Locality of relative symplectic cohomology for com- plete embeddings”. In:Compos. Math.159.12 (2023), pp. 2551–2637.doi:10 . 1112 / S0010437X23007492
work page 2023
-
[37]
Pseudo holomorphic curves in symplectic manifolds
M. Gromov. “Pseudo holomorphic curves in symplectic manifolds”. In:Inventiones mathe- maticae82 (1985), pp. 307–347
work page 1985
-
[38]
P. Hacking, J. Tevelev, and G. Urz´ ua. “Flipping surfaces”. In:J. Algebr. Geom.26.2 (2017), pp. 279–345.doi:10.1090/jag/682
-
[39]
R. Hind. “Lagrangian spheres inS 2 ×S 2”. In:Geom. Funct. Anal.14.2 (2004), pp. 303–318. doi:10.1007/s00039-004-0459-6
-
[40]
Symplectomophism groups of non-compact manifolds, orbifold balls, and a space of Lagrangians
R. Hind, M. Pinsonnault, and W. Wu. “Symplectomophism groups of non-compact manifolds, orbifold balls, and a space of Lagrangians”. In:J. Symplectic Geom.14(1) (2016), pp. 203– 226
work page 2016
-
[41]
On genericity for holomorphic curves in four- dimensional almost-complex manifolds
H. Hofer, V. Lizan, and J.-C. Sikorav. “On genericity for holomorphic curves in four- dimensional almost-complex manifolds”. In:J. Geom. Anal.7.1 (1997), pp. 149–159.doi: 10.1007/BF02921708
-
[42]
Microlocal Sheaves on Pinwheels
D. Karabas.Microlocal Sheaves on Pinwheels. 2018. arXiv:1810.09021 [math.SG]
work page internal anchor Pith review Pith/arXiv arXiv 2018
-
[43]
A. Keating, I. Smith, and M. Wemyss.Splitting symplectic monodromy. 2026. arXiv:2601. 20438 [math.SG]
work page 2026
-
[44]
Bounds on Embeddings of Rational Homology Balls in Symplectic 4-manifolds
T. Khodorovskiy.Bounds on Embeddings of Rational Homology Balls in Symplectic 4- manifolds. 2013. arXiv:1307.4321 [math.SG]
work page internal anchor Pith review Pith/arXiv arXiv 2013
-
[45]
T. Khodorovskiy.Symplectic Rational Blow-up. 2013. arXiv:1303.2581 [math.SG]
work page internal anchor Pith review Pith/arXiv arXiv 2013
-
[46]
Threefolds and deformations of surface singularities
J. Koll´ ar and N. I. Shepherd-Barron. “Threefolds and deformations of surface singularities”. In:Invent. Math.91.2 (1988), pp. 299–338.doi:10.1007/BF01389370. REFERENCES 67
-
[47]
Parametrized ring-spectra and the nearby Lagrangian conjecture
T. Kragh. “Parametrized ring-spectra and the nearby Lagrangian conjecture”. In:Geom. Topol.17.2 (2013), pp. 639–731.doi:10.2140/gt.2013.17.639
-
[48]
The symplectic topology of some rational homology balls
Y. Lekili and M. Maydanskiy. “The symplectic topology of some rational homology balls”. In:Comment. Math. Helv.89.3 (2014), pp. 571–596.doi:10.4171/CMH/327
-
[49]
E. Lerman. “Symplectic cuts”. In:Math. Res. Lett.2.3 (1995), pp. 247–258.doi:10.4310/ MRL.1995.v2.n3.a2
work page 1995
-
[50]
Lagrangian spheres, symplectic surfaces and the symplectic mapping class group
T.-J. Li and W. Wu. “Lagrangian spheres, symplectic surfaces and the symplectic mapping class group”. In:Geom. Topol.16.2 (2012), pp. 1121–1169.doi:10.2140/gt.2012.16.1121
-
[51]
On almost complex embeddings of rational homology balls
P. Lisca and A. Parma. “On almost complex embeddings of rational homology balls”. In: Frontiers in geometry and topology. Summer school and research conference, The Abdus Salam International Centre for Theoretical Physics, Trieste, Italy, August 1–12, 2022. Providence, RI: American Mathematical Society (AMS), 2024, pp. 183–193.doi:10.1090/pspum/109/ 01995
-
[52]
On Stein rational balls smoothly but not symplectically embedded inCP 2
P. Lisca and A. Parma. “On Stein rational balls smoothly but not symplectically embedded inCP 2”. In:Bull. Lond. Math. Soc.54.3 (2022), pp. 949–960.doi:10.1112/blms.12607
-
[53]
D. McDuff and D. Salamon.J-holomorphic curves and symplectic topology. Vol. 52. American Mathematical Society Colloquium Publications. American Mathematical Society, Providence, RI, 2004, pp. xii+669.doi:10.1090/coll/052
-
[54]
D. McDuff and D. Salamon.Introduction to symplectic topology. 3rd edition. Vol. 27. Oxf. Grad. Texts Math. Oxford: Oxford University Press, 2016
work page 2016
-
[55]
Ellipsoidal superpotentials and singular curve counts
D. McDuff and K. Siegel. “Ellipsoidal superpotentials and singular curve counts”. In:Int. Math. Res. Not.2025.21 (2025). Id/No rnaf285, p. 37.doi:10.1093/imrn/rnaf285
-
[56]
Singular algebraic curves and infinite symplectic staircases
D. McDuff and K. Siegel. “Singular algebraic curves and infinite symplectic staircases”. In: Invent. Math.242.2 (2025), pp. 387–459.doi:10.1007/s00222-025-01359-4
-
[57]
On certain Lagrangian submanifolds ofS 2 ×S 2 andCP n
J. Oakley and M. Usher. “On certain Lagrangian submanifolds ofS 2 ×S 2 andCP n”. In: Algebr. Geom. Topol.16.1 (2016), pp. 149–209.doi:10.2140/agt.2016.16.149
-
[58]
Equivariant embeddings of rational homology balls
B. Owens. “Equivariant embeddings of rational homology balls”. In:Q. J. Math.69.3 (2018), pp. 1101–1121.doi:10.1093/qmath/hay016
-
[59]
Smooth, nonsymplectic embeddings of rational balls in the complex projective plane
B. Owens. “Smooth, nonsymplectic embeddings of rational balls in the complex projective plane”. In:Q. J. Math.71.3 (2020), pp. 997–1007.doi:10.1093/qmathj/haaa013
-
[60]
Milnor fibers and symplectic fillings of quotient surface singularities
H. Park, J. Park, D. Shin, and G. Urz´ ua. “Milnor fibers and symplectic fillings of quotient surface singularities”. In:Adv. Math.329 (2018), pp. 1156–1230.doi:10.1016/j.aim.2018. 03.002
-
[61]
L. Polterovich and F. Schlenk.Lagrangian knots and unknots – an essay.With an appendix by G. Dimitroglou Rizell. 2024. arXiv:2406.15967 [math.SG]
-
[62]
Graded Lagrangian submanifolds
P. Seidel. “Graded Lagrangian submanifolds”. In:Bull. Soc. Math. Fr.128.1 (2000), pp. 103– 149.doi:10.24033/bsmf.2365
-
[63]
Lagrangian two-spheres can be symplectically knotted
P. Seidel. “Lagrangian two-spheres can be symplectically knotted”. In:J. Differ. Geom.52.1 (1999), pp. 145–171.doi:10.4310/jdg/1214425219. 68 REFERENCES
-
[64]
Symplectic triangle inequality
V. Shevchishin and G. Smirnov. “Symplectic triangle inequality”. In:Proc. Am. Math. Soc. 148.4 (2020), pp. 1389–1397.doi:10.1090/proc/14842
-
[65]
Four dimensions from two in symplectic topology
M. Symington. “Four dimensions from two in symplectic topology”. In:Topology and geome- try of manifolds (Athens, GA, 2001). Vol. 71. Proc. Sympos. Pure Math. Amer. Math. Soc., Providence, RI, 2003, pp. 153–208.doi:10.1090/pspum/071/2024634
-
[66]
Generalized symplectic rational blowdowns
M. Symington. “Generalized symplectic rational blowdowns”. In:Algebr. Geom. Topol.1 (2001), pp. 503–518
work page 2001
-
[67]
M. Symington. “Symplectic rational blowdowns”. In:J. Differ. Geom.50.3 (1998), pp. 505– 518.doi:10.4310/jdg/1214424968
-
[68]
G. Urz´ ua.Negative continued Fractions in Birational Geometry: A guide to Degenerations of Surfaces with Wahl Singularities. 2025
work page 2025
-
[69]
G. Urz´ ua and J. P. Z´ u˜ niga.The birational geometry of Markov numbers. 2025. arXiv:2310. 17957 [math.AG]
work page 2025
-
[70]
C. Wendl.Holomorphic curves in low dimensions. From symplectic ruled surfaces to planar contact manifolds. Vol. 2216. Lect. Notes Math. Berlin: Springer, 2018.doi:10.1007/978- 3-319-91371-1
-
[71]
Exact Lagrangians inA n-surface singularities
W. Wu. “Exact Lagrangians inA n-surface singularities”. In:Math. Ann.359.1-2 (2014), pp. 153–168.doi:10.1007/s00208-013-0993-3
-
[72]
On an exotic Lagrangian torus inCP 2
W. Wu. “On an exotic Lagrangian torus inCP 2”. In:Compos. Math.151.7 (2015), pp. 1372– 1394.doi:10.1112/S0010437X14007945. Nikolas Adaloglou, imj-prg, Sorbonne Universit ´e et Universit´e Paris Cit´e, CNRS Email address:adaloglou@imj-prg.fr Gerard Bargall´o i G ´omez, Institut f¨ur Mathematik Humboldt-Universit¨at zu Berlin Email address:gerard.bargallo.i...
discussion (0)
Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.