The flag-complex canonical-representation lower-bound conjecture

From papers

Let Δ\Delta be a flag complex with βk1(Δ)=a>0\beta_{k-1}(\Delta)=a>0. Suppose that

a=(akk) ⁣k+(ak1k1) ⁣k1++(aksks) ⁣ksa=\binom{a_k}{k}_{\!k}+\binom{a_{k-1}}{k-1}_{\!k-1}+\dots+\binom{a_{k-s}}{k-s}_{\!k-s}

is the (k,k)(k,k)-canonical representation of aa.

Canonical-representation lower-bound conjecture. For every i0i\geq 0,

fi1(Δ)(ak+ki) ⁣k+(ak1+k1i1) ⁣k1++(aks+ksis) ⁣ks.f_{i-1}(\Delta)\geq\binom{a_k+k}{i}_{\!k}+\binom{a_{k-1}+k-1}{i-1}_{\!k-1}+\dots+\binom{a_{k-s}+k-s}{i-s}_{\!k-s}.

This conjecture would give a quantitative refinement of Meshulam's theorem for flag complexes in all dimensions and would imply the subsequent Turán-complex lower-bound conjecture.

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Sources & referencesView supporting material

Primary source

Kai Fong Ernest Chong and Eran Nevo, “Flag complexes and homology”, arXiv:1908.08308 (2019).

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