Almost h-positivity conjecture for rank-selected subword-order homology

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Let AA be an alphabet of size n≥2n\ge 2, and let SnS_n act on A∗A^* by permuting the alphabet. A rank-selected subposet is obtained by retaining words whose ranks belong to a finite nonempty set. Let S(n−1,1)S_{(n-1,1)} be the reflection representation of SnS_n, and set T2(n)={hλ:λ=(n−r,1r), r≥2}T_2(n)=\{h_\lambda: \lambda=(n-r,1^r),\ r\ge 2\}. Almost h-positivity conjecture. The homology of any finite nonempty rank-selected subposet of subword order on A∗A^*, plus or minus one copy of S(n−1,1)S_{(n-1,1)}, is a permutation module. Its Frobenius characteristic is hh-positive and supported on T2(n)T_2(n).

References

Primary source

Sheila Sundaram, “The reflection representation in the homology of subword order”, arXiv:2006.13367 (2021).

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