The sorting-alternating quotient conjecture for subword complexes

Let QQ be a word and let ω\omega be an element of a Coxeter group. For the non-empty subword complex SC(Q,ω)\mathcal{SC}(Q,\omega), let [e,ω][e,\omega] be the corresponding weak-order interval and let Q,ω\equiv_{Q,\omega} be the subword complex equivalence. The word QQ is sorting when it contains a reduced expression for the longest element ω\omega_\circ, and it is alternating when every pair of non-commuting generators alternates within QQ. Sorting-alternating quotient conjecture. If QQ is sorting and alternating, then the Hasse diagram of the lattice quotient [e,ω]/Q,ω[e,\omega]/\equiv_{Q,\omega} is isomorphic to the graph of extremal increasing flips between acyclic facets of SC(Q,ω)\mathcal{SC}(Q,\omega). In the sorting case all acyclic facets are strongly acyclic, so this specializes the alternating-word quotient conjecture; the source gives no resolution status.

Sources & referencesView supporting material

Primary source

Nantel Bergeron, Noémie Cartier, Cesar Ceballos and Vincent Pilaud, “Lattices of acyclic pipe dreams”, arXiv:2303.11025 (2025).

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