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| | Category Theory |
 | | Indeed, from a categorical point of view, a set-theoretical cartesian product, a direct product of groups, a direct product of abelian groups, a product of topological spaces and a conjunction of propositions in a deductive system are all instances of a categorical concept: the categorical product. |
 | | First, using the axiomatic method and the categorical language, Grothendieck defined abstractly types of categories, e.g., additive and abelian categories, showed how to perform various constructions in these categories and proved various results for them. |
 | | Indeed, categorical logic, the study of logic with the help of categorical means, has been around for about 30 years now and is still vigorous. |
| plato.stanford.edu /entries/category-theory (7029 words) |
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