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Real link Floer homology
Pith reviewed 2026-05-08 13:37 UTC · model grok-4.3
The pith
Real link Floer homology is defined for strongly invertible and doubly periodic links in real 3-manifolds.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
We define real link Floer homology for strongly invertible and doubly periodic links in closed real 3-manifolds with connected fixed sets, which generalizes real Heegaard Floer homology and real sutured Heegaard Floer homology. We give a combinatorial description of the theory in S^3 via real grid diagrams and use it to investigate structural properties of the theory as well as properties of strongly invertible knots.
What carries the argument
Real grid diagrams, which are grid presentations of links in S^3 that are equivariant under a fixed involution and generate a chain complex whose homology is the real link Floer homology.
If this is right
- The homology supplies a combinatorial invariant for strongly invertible links in S^3 that can be calculated directly from grid diagrams.
- The theory applies to all closed real 3-manifolds with connected fixed sets and recovers the earlier real Heegaard Floer theories in the appropriate special cases.
- Explicit computations become feasible for small knots, producing concrete homology groups and revealing patterns in the data for more than fifty examples.
- Structural properties such as behavior under connected sums or other operations on the links can be read off from the chain complex.
Where Pith is reading between the lines
- The observed patterns in the computed examples for small knots may point to a relationship between the rank of the homology and the symmetry type of the knot.
- Because the construction is combinatorial, it opens the possibility of machine-assisted searches for knots whose real link Floer homology detects previously invisible features of strong inversions.
- The generalization to real 3-manifolds suggests the theory could be used to study equivariant problems in other Floer-type invariants that have real versions.
Load-bearing premise
The homology groups obtained from the construction do not depend on the choice of real Heegaard diagram or real grid diagram and remain unchanged when the link is modified by the allowed real moves.
What would settle it
Two different real grid diagrams for the same strongly invertible knot whose associated chain complexes have different homology groups, or a sequence of real link moves that alters the computed homology.
Figures
read the original abstract
In this paper, we define real link Floer homology for strongly invertible and doubly periodic links in closed real $3$-manifolds with connected fixed sets, which generalizes real Heegaard Floer homology and real sutured Heegaard Floer homology. We give a combinatorial description of the theory in $S^3$ via real grid diagrams and use it to investigate structural properties of the theory as well as properties of strongly invertible knots. A computer implementation was written by Zhenkun Li. An appendix including real grid homology for 50+ small knots is made jointly by Zhenkun Li and the author, from which we observe several interesting phenomenon.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper defines real link Floer homology for strongly invertible and doubly periodic links in closed real 3-manifolds with connected fixed sets, generalizing real Heegaard Floer homology and real sutured Heegaard Floer homology. It supplies a combinatorial description in S^3 via real grid diagrams, uses this to investigate structural properties of the theory and of strongly invertible knots, includes a computer implementation, and provides an appendix with real grid homology computations for over 50 small knots.
Significance. If the invariance under diagram changes is established, the construction would furnish a new Floer-theoretic invariant adapted to real symmetries, extending existing real Heegaard Floer theories to links and enabling computational study of strongly invertible knots. The combinatorial grid-diagram approach together with the explicit computer implementation and tabulated examples constitute concrete strengths that would make the invariant immediately usable for further calculations and conjectures.
major comments (2)
- [Section describing the combinatorial chain complex and its invariance (the section immediately following the definition)] The central claim that the homology is a link invariant rests on the assertion that the chain complex defined from a real grid diagram is independent of the choice of diagram. The text does not supply the required case-by-case verification that every real analogue of a grid move (real stabilizations, real commutations, and real Reidemeister-type moves compatible with the strong inversion or double periodicity) induces a chain homotopy equivalence; without these explicit homotopy equivalences the homology remains diagram-dependent rather than an invariant of the link.
- [Introduction and the section on the definition of real link Floer homology] The generalization from real Heegaard Floer homology to the link setting is stated in the abstract and introduction, yet the manuscript supplies no derivation steps showing how the real link complex reduces to the known real Heegaard or sutured complexes when the link is a knot or when the diagram is a Heegaard diagram; this reduction is load-bearing for the claim that the new theory is a genuine generalization.
minor comments (2)
- Notation for the real generators and the differential counting real holomorphic disks (or their combinatorial analogues) should be introduced with a single consistent table or list of symbols to avoid ambiguity when the same symbols appear in both the geometric and combinatorial descriptions.
- [Appendix] The appendix computations are valuable; each table should include a brief statement of the diagram used and the grading conventions so that readers can reproduce the entries from the combinatorial definition.
Simulated Author's Rebuttal
We thank the referee for the careful reading and constructive comments on our manuscript. The two major points raised concern the explicit verification of invariance under real grid moves and the detailed reduction to the known real Heegaard and sutured theories. We address each below and will revise the manuscript to strengthen these aspects while retaining the combinatorial and computational contributions.
read point-by-point responses
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Referee: [Section describing the combinatorial chain complex and its invariance (the section immediately following the definition)] The central claim that the homology is a link invariant rests on the assertion that the chain complex defined from a real grid diagram is independent of the choice of diagram. The text does not supply the required case-by-case verification that every real analogue of a grid move (real stabilizations, real commutations, and real Reidemeister-type moves compatible with the strong inversion or double periodicity) induces a chain homotopy equivalence; without these explicit homotopy equivalences the homology remains diagram-dependent rather than an invariant of the link.
Authors: We agree that explicit verification of invariance is necessary to establish the homology as a true link invariant. The manuscript defines the real grid moves and asserts invariance by analogy with the non-real grid homology literature, but we acknowledge that the full case-by-case construction of chain homotopy equivalences (for real stabilizations, commutations, and symmetry-compatible Reidemeister moves) is not written out in detail. In the revised version we will insert a new subsection immediately after the definition of the chain complex. This subsection will construct the required homotopy equivalences explicitly, adapting the standard arguments from Manolescu–Ozsváth–Sarkar and subsequent grid-homology papers to the real symmetric setting while preserving the real involution on the complex. These additions will make the invariance rigorous without changing the overall combinatorial framework. revision: yes
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Referee: [Introduction and the section on the definition of real link Floer homology] The generalization from real Heegaard Floer homology to the link setting is stated in the abstract and introduction, yet the manuscript supplies no derivation steps showing how the real link complex reduces to the known real Heegaard or sutured complexes when the link is a knot or when the diagram is a Heegaard diagram; this reduction is load-bearing for the claim that the new theory is a genuine generalization.
Authors: We appreciate the referee’s emphasis on making the generalization explicit. By construction, a real grid diagram for a strongly invertible knot specializes to a real Heegaard diagram of the knot complement (or the closed manifold), with generators, differentials, and gradings matching those of real Heegaard Floer homology; the sutured case follows similarly when the diagram is viewed as a sutured Heegaard diagram. To render this reduction transparent, we will add a short paragraph in the introduction and a dedicated remark in the definition section that spells out the correspondence between the real link complex and the existing real Heegaard/sutured complexes in the knot and Heegaard-diagram special cases. This clarification will be purely expository and will not alter the definitions or results. revision: yes
Circularity Check
No circularity: definition via real grid diagrams is independent of inputs.
full rationale
The paper defines real link Floer homology directly from real grid diagrams for strongly invertible and doubly periodic links, generalizing prior real Heegaard Floer theories without self-referential equations or fitted parameters renamed as predictions. No load-bearing step reduces the homology to its own construction by definition, self-citation chain, or ansatz smuggling. Invariance under diagram moves is a standard proof obligation in such combinatorial Floer theories and does not constitute circularity per the enumerated patterns. The appendix computations provide external verification content rather than tautological support. This is a normal non-finding for a definitional generalization paper.
Axiom & Free-Parameter Ledger
axioms (1)
- domain assumption Real Heegaard Floer homology and real sutured Heegaard Floer homology are well-defined and invariant as previously constructed.
Reference graph
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