QED

I think it is said that Gauss had ten different proofs for the law of quadratic reciprocity. Any good theorem should have several proofs, the more the better. For two reasons: usually, different proofs have different strengths and weaknesses, and they generalize in different directions - they are not just repetitions of each other.

Sir Michael Atiyah, in Martin Raussen & Christian Skau, Interview with Michael Atiyah and Isadore Singer (24 mei 2004)

Dit interview had plaats in Oslo naar aanleiding van de Abelprijs die Atiyah en Singer ontvingen voor “the discovery and the proof of the Index Theorem connecting geometry and analysis in a surprising way”. Het citaat gaat over drie verschillende bewijzen die Atiyah leverde voor de index-stelling. Het citaat gaat verder:

And that is certainly the case with the proofs that we came up with. There are different reasons for the proofs, they have different histories and backgrounds. Some of them are good for this application, some are good for that application. They all shed light on the area. If you cannot look at a problem from different directions, it is probably not very interesting; the more perspectives, the better!