On collapsible ball pairs
نویسندگان
چکیده
منابع مشابه
Knots in Collapsible and Non-Collapsible Balls
We construct the first explicit example of a simplicial 3-ball B15,66 that is not collapsible. It has only 15 vertices. We exhibit a second 3-ball B12,38 with 12 vertices that is collapsible and not shellable, but evasive. Finally, we present the first explicit triangulation of a 3-sphere S18,125 (with only 18 vertices) that is not locally constructible. All these examples are based on knotted ...
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Let (G;N) be a pair of groups. In this article, first we con-struct a relative central extension for the pair (G;N) such that specialtypes of covering pair of (G;N) are homomorphic image of it. Second, weshow that every perfect pair admits at least one covering pair. Finally,among extending some properties of perfect groups to perfect pairs, wecharacterize covering pairs of a perfect pair (G;N)...
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ژورنال
عنوان ژورنال: Illinois Journal of Mathematics
سال: 1968
ISSN: 0019-2082
DOI: 10.1215/ijm/1256054109