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The formal definition of a category implies the existence of an identity arrow for each object. Because semi-groups do not have an identity element, I guess we should not call them "category of semigroups". Shall we not call them "questionable category of semigroups" or something in that spirit? — Preceding unsigned comment added by 178.197.234.69 ( talk) 14:12, 24 October 2016 (UTC)
The figure seems to show an object {0} that is terminal, but not initial (no arrows from {0} to any of the other elements of A). — Preceding unsigned comment added by 98.207.232.114 ( talk) 22:25, 18 February 2018 (UTC)
![]() | This ![]() It is of interest to the following WikiProjects: | ||||||||||
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The formal definition of a category implies the existence of an identity arrow for each object. Because semi-groups do not have an identity element, I guess we should not call them "category of semigroups". Shall we not call them "questionable category of semigroups" or something in that spirit? — Preceding unsigned comment added by 178.197.234.69 ( talk) 14:12, 24 October 2016 (UTC)
The figure seems to show an object {0} that is terminal, but not initial (no arrows from {0} to any of the other elements of A). — Preceding unsigned comment added by 98.207.232.114 ( talk) 22:25, 18 February 2018 (UTC)