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arXiv · 2309.14261

The $s$-weak order and $s$-permutahedra II: The combinatorial complex of pure intervals

Cesar Ceballos·Viviane Pons
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Abstract

This paper introduces the geometric foundations for the study of the $s$-permutahedron and the $s$-associahedron, two objects that encode the underlying geometric structure of the $s$-weak order and the $s$-Tamari lattice. We introduce the $s$-permutahedron as the complex of pure intervals of the $s$-weak order, present enumerative results about its number of faces, and prove that it is a combinatorial complex. This leads, in particular, to an explicit combinatorial description of the intersection of two faces. We also introduce the $s$-associahedron as the complex of pure $s$-Tamari intervals of the $s$-Tamari lattice, show some enumerative results, and prove that it is isomorphic to a well chosen $\nu$-associahedron. Finally, we present three polytopality conjectures, evidence supporting them, and some hints about potential generalizations to other finite Coxeter groups.

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Cesar Ceballos, Viviane Pons. 2023-09-25. The $s$-weak order and $s$-permutahedra II: The combinatorial complex of pure intervals. https://doi.org/10.37236/12438

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