Generalized lower bound conjecture for complexes with bounded missing-face dimension

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Let dotobreak≥0d ot obreak\geq 0 and 0<i≤d+10<i\leq d+1 be integers. Let C(i,d)\mathcal{C}(i,d) be the family of dd-dimensional simplicial complexes with nonzero reduced dd-homology and no missing faces of dimension greater than ii. Write d+1=qi+rd+1=qi+r with q≥0q\geq 0 and 1≤r≤i1\leq r\leq i, and let S(i,d)S(i,d) be the join of qq copies of the boundary of the ii-simplex and the boundary of the rr-simplex. Let f⁡j(Δ)\operatorname{f}_j(\Delta) denote the number of jj-dimensional faces of Δ\Delta. Generalized lower bound conjecture. For Δ∈C(i,d)\Delta\in\mathcal{C}(i,d),

f⁡j(Δ)≥f⁡j(S(i,d))\operatorname{f}_j(\Delta)\geq \operatorname{f}_j(S(i,d))

for every jj. Moreover, if equality is attained for every jj, then Δ=S(i,d)\Delta=S(i,d). The source presents this as a conjectural strengthening of known extremal results; the condition i∣(d+1)i\mid(d+1) is noted as an artifact of the proof in the surrounding theorem, so the full assertion remains open.

References

Primary source

Eran Nevo, “Remarks on missing faces and generalized lower bounds on face numbers”, arXiv:0810.5487 (2009).

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