The Lefschetz-to-gg hierarchy conjecture for homology spheres

Let LL be a homology (d1)(d-1)-sphere. Write (ab)\binom{a}{b} only through the interval notation in the claim, where [a,b][a,b] denotes the corresponding set of integers, and let

\Delta(L)$ be the relevant symmetric shifting of $L$. **Lefschetz-to-$g$ hierarchy conjecture.** The following assertions hold for $L$: (1) If $S\in\Delta(L)$, $|S|=k\leq\lfloor d/2\rfloor$ and $S\cap[d-k+1]=\emptyset$, then $S\cup[k+2,d-k+1]\in\Delta(L)$; this is equivalent to

\Delta(K)\subseteq\Delta(d)and,inthesymmetriccase,toand, in the symmetric case, toLbeingstrongLefschetz.(2)Ifbeing strong-Lefschetz. (2) IfS\in\Delta(L),, |S|=k<\lfloor d/2\rfloorandandS\cap[d-k+1]=\emptyset,then, then S\cup[\lceil d/2\rceil+2,d-k+1]\in\Delta(L);inthesymmetriccase,thisisequivalentto; in the symmetric case, this is equivalent to LbeingweaklyweakLefschetz.(3)being weakly weak-Lefschetz. (3)g(L)isanis anM$-vector. The paper presents these assertions as a hierarchy in which each assertion implies the next; the source does not state that the hierarchy has been resolved.

Sources & referencesView supporting material

Primary source

Eric Babson and Eran Nevo, “Lefschetz Properties and Basic Constructions on Simplicial Spheres”, arXiv:0802.1058 (2008).

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