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According to the Nobel Prize-winning physicist Richard Feynman 
 (1985), mathematicians designate any
Theorem as ``trivial'' once a proof has been obtained--no matter how difficult the theorem was to prove in the
first place. There are therefore exactly two types of true mathematical propositions: trivial ones, and those which have not
yet been proven.
See also Proof, Theorem
References
Feynman, R. P. and Leighton, R.  Surely You're Joking, Mr. Feynman!  New York: Bantam Books, 1985.