On Weakly Contractible Non-Contractible Finite Topological Spaces of Ten Points
Abstract
Cianci and Ottina proved that a homotopically trivial non-contractible finite T0-space has at least nine points, and classified such spaces with exactly nine points. We complete the classification for ten points. The main tool is the notion of a naked pair: a relation c<a between a minimal and a maximal point that does not factor through a middle point. We show that minimal homotopically trivial spaces with at most ten points have no naked pairs. This turns minimality into simple conditions on the incidences between the three levels of the space and, together with two lemmas of Cianci and Ottina and an Euler characteristic count, reduces the classification to short case analyses. No such space exists with one or two middle points; there are exactly six with three middle points, forming three types and their order-duals, and exactly four with four middle points. All ten spaces have height two, an antichain of middle points and collapsible order complexes, and the count is confirmed by an exhaustive computer enumeration. We also show that the absence of naked pairs persists up to seventeen points but not beyond, and that height three already occurs at eleven points.
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BibTeX
@misc{das2026weakly,
title = {{On Weakly Contractible Non-Contractible Finite Topological Spaces of Ten Points}},
author = {Ponaki Das and Sainkupar Marwein Mawiong},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2605.06155},
eprint = {2605.06155},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2605.06155},
}
RIS
TY - UNPB
TI - On Weakly Contractible Non-Contractible Finite Topological Spaces of Ten Points
AU - Ponaki Das
AU - Sainkupar Marwein Mawiong
PY - 2026
DA - 2026/10/05
PB - arXiv
DO - 10.48550/arxiv.2605.06155
UR - https://arxiv.org/abs/2605.06155
AB - Cianci and Ottina proved that a homotopically trivial non-contractible finite T_0-space has at least nine points, and classified such spaces with exactly nine points. We complete the classification for ten points. The main tool is the notion of a naked pair: a relation c<a between a minimal and a maximal point that does not factor through a middle point. We show that minimal homotopically trivial spaces with at most ten points have no naked pairs. This turns minimality into simple conditions on the incidences between the three levels of the space and, together with two lemmas of Cianci and Ottina and an Euler characteristic count, reduces the classification to short case analyses. No such space exists with one or two middle points; there are exactly six with three middle points, forming three types and their order-duals, and exactly four with four middle points. All ten spaces have height two, an antichain of middle points and collapsible order complexes, and the count is confirmed by an exhaustive computer enumeration. We also show that the absence of naked pairs persists up to seventeen points but not beyond, and that height three already occurs at eleven points.
ER -