The N-filling formula for unoriented knot Floer homology

From papers

Let YY be a 33-manifold and KYK\subset Y a knot, with meridian μ\mu. Let NN be the twisted II-bundle over the Klein bottle, and let YNμY_N^\mu be the N-filling of YintN(K)Y\setminus\operatorname{int}N(K) with respect to μ\mu, obtained by gluing NN so that its homological longitude maps to μ\mu. Let HFK2(Y,K)HFK'_2(Y,K) be the proposed unoriented knot Floer homology, and let HF^\widehat{HF} denote Heegaard Floer homology. N-filling conjecture. There is an isomorphism

HF^(YNμ)HFK2(Y,K)HF^(Y)HF^(Y).\widehat{HF}(Y_N^\mu)\cong HFK'_2(Y,K)\oplus\widehat{HF}(Y)\oplus\widehat{HF}(Y).

This conjecture connects the proposed knot Floer invariant with the NN-filling construction used in the study of graph-manifold L-space questions; the supplied source gives no resolution status.

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Primary source

Deeparaj Bhat, Zhenkun Li and Fan Ye, “Instanton 2-torsion and fibered knots”, arXiv:2512.24206 (2025).

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