English

Cubical convex ear decompositions

Combinatorics 2020-07-08 v3

Abstract

We consider the problem of constructing a convex ear decomposition for a poset. The usual technique, first used by Nyman and Swartz, starts with a CL-labeling and uses this to shell the `ears' of the decomposition. We axiomatize the necessary conditions for this technique as a "CL-ced" or "EL-ced". We find an EL-ced of the d-divisible partition lattice, and a closely related convex ear decomposition of the coset lattice of a relatively complemented group. Along the way, we construct new EL-labelings of both lattices. The convex ear decompositions so constructed are formed by face lattices of hypercubes. We then proceed to show that if two posets P_1 and P_2 have convex ear decompositions (CL-ceds), then their products P_1 \times P_2, P_1 \lrtimes P_2, and P_1 \urtimes P_2 also have convex ear decompositions (CL-ceds). An interesting special case is: if P_1 and P_2 have polytopal order complexes, then so do their products.

Cite

@article{arxiv.0709.2793,
  title  = {Cubical convex ear decompositions},
  author = {Russ Woodroofe},
  journal= {arXiv preprint arXiv:0709.2793},
  year   = {2020}
}

Comments

33 pages. v2 shows that products of spaces with ceds have ceds (which was a question in v1), improves exposition. v3 further improves exposition and corrects typos

R2 v1 2026-06-21T09:18:38.689Z