Sorry, if it's not too late please post this one instead: From: John Baez <baez@math.ucr.edu> Date: Tue, Sep 14, 2010 at 3:33 PM Subject: Evil To: categories <categories@mta.ca> David wrote: Jean Benabou wrote:

...

Maybe my english isn't so "beautiful", but in all cases where "evil" has been used, what is wrong with "wrong" instead?

I'm not so enamoured with the use of the word 'evil', but it seems to

be more entrenched than perhaps it was intended, namely as a joke.

It's supposed to be funny, but I'm glad to see it become entrenched. Why? First, it has a very specific meaning. A property of objects of some category C is said to be "evil" if it holds for some object x of C but not some isomorphic object y. More generally: a property of objects of some n-category is "evil" if it holds for some object x but not some equivalent object y. For details, see: http://ncatlab.org/nlab/show/evil Second, it captures the interesting state of affairs in category theory where some definitions can be well-formed yet somehow "suboptimal" because equations were used when isomorphisms should have been specified. "Wrong" doesn't work here, since mathematicians use it in other important ways: for example, "false", "incorrect" or "inappropriate". "Evil" is, to the best of my knowledge, never used in mathematics except in this one technical sense. If anybody finds the term "evil" upsettingly strong, I suggest "naughty" as an alternative. Best, jb [For admin and other information see: http://www.mta.ca/~cat-dist/ ]