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Earlier someone was asking about the category "Ens" described in Categories for the Working Mathematician. My question is more basic: What does Ens stand for? Most of the categories have names that are self explanatory, and maybe this one does too. But for the life of me I can't think of it, and a Google search was no help.

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    The school Yuval refers to is so superior that it even gets a final "e": École Normale Supérieure. @Matt: And I reall$y$, reall$y$ hope he is kidding!2011-06-19

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It stands for "ensembles". Here is the other question, btw.

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    @Matt: I thi$n$k it is obvious, but o$n$ly because I happened to know that the French for set (in the mathematical sense!) is ensemble. Perhaps Mac Lane neglected to explain it because the working mathematician of the time was expected to know French?2011-06-18