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A 0-groupoid is a set. This terminology may seem strange at first, but it is very helpful to see sets as the beginning of a sequence of concepts: sets, groupoids, 2-groupoids, 3-groupoids, etc. Doing so reveals patterns such as the periodic table. (It also sheds light on the theory of homotopy groups and n-stuff.)
For example, there should be a -groupoid of -groupoids; this is the underlying groupoid of the category of sets. Then a groupoid enriched over this is a -groupoid (more precisely, a locally small groupoid). Furthermore, an enriched category is a category (or -category), so a -groupoid is the same as a 0-category.
One can continue to define a (-1)-groupoid(−1)-groupoid? to be a truth value and a (-2)-groupoid(−2)-groupoid? to be a triviality (that is, there is exactly one).
Revision on June 30, 2010 at 21:59:17 by Toby Bartels See the history of this page for a list of all contributions to it.