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What is your favorite ADE-style classification? Here ADE style is to be understood in a very broad sense. A classification which is not precisely ADE, but roughly related is fine. For example simple complex Lie algebras, or affine Weyl groups would be okay.

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Isn't this question just a subjective version of this one? mathoverflow.net/questions/6781/ade-type-dynkin-diagrams –  j.c. Nov 4 '10 at 10:30
I agree with jc: this question is a duplicate. (Also the linked to question does not use the word "favorite", the usage of which in a MO question I have come to deprecate.) –  Pete L. Clark Nov 4 '10 at 10:42
Okay, you are right, I did not spot this question before. –  Jan Weidner Nov 4 '10 at 10:44