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.