New families of highly neighborly centrally symmetric spheres

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  • Isabella Novik
  • Hailun Zheng

Jockusch [J. Combin. Theory Ser. A 72 (1995), pp. 318-321] constructed an infinite family of centrally symmetric (cs, for short) triangulations of 3-spheres that are cs-2-neighborly. Recently, Novik and Zheng [Adv. Math. 370 (2020), 16 pp.] extended Jockusch's construction: for all d and n > d, they constructed a cs triangulation of a d-sphere with 2n vertices, Δdn, that is cs-⌈d/2⌉-neighborly. Here, several new cs constructions, related to Δdn, are provided. It is shown that for all k > 2 and a sufficiently large n, there is another cs triangulation of a (2k − 1)-sphere with 2n vertices that is cs-k-neighborly, while for k = 2 there are Ω(2n) such pairwise non-isomorphic triangulations. It is also shown that for all k > 2 and a sufficiently large n, there are Ω(2n) pairwise non-isomorphic cs triangulations of a (2k − 1)-sphere with 2n vertices that are cs-(k − 1)-neighborly. The constructions are based on studying facets of Δdn, and, in particular, on some necessary and some sufficient conditions similar in spirit to Gale's evenness condition. Along the way, it is proved that Jockusch's spheres Δ3n are shellable and an affirmative answer to Murai-Nevo's question about 2-stacked shellable balls is given.

Original languageEnglish
JournalTransactions of the American Mathematical Society
Volume375
Issue number6
Pages (from-to)4445-4475
ISSN0002-9947
DOIs
Publication statusPublished - 2022

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