Theorem
A statement which can be demonstrated to be true by accepted mathematical operations and arguments. In general, a theoremis an embodiment of some general principle that makes it part of a larger theory.
According to the Nobel Prize-winning physicist Richard Feynman 
(1985), any theorem, no matter howdifficult to prove in the first place, is viewed as ``Trivial'' by mathematicians once it has been proven. Therefore, there are exactly two types of mathematical objects: Trivial ones, and those which have not yet beenproven.
References
Feynman, R. P. and Leighton, R. Surely You're Joking, Mr. Feynman! New York: Bantam Books, 1985.
- Apparatus Function
- Appell Hypergeometric Function
- Appell Polynomial
- Appell Transformation
- Apple
- Approximately Equal
- Approximation Theory
- Apéry's Constant
- Arakelov Theory
- Arbelos
- Arborescence
- Arboricity
- Arc
- Arch
- Archimedean Solid
- Archimedean Solid Stellation
- Archimedean Spiral
- Archimedean Spiral Inverse Curve
- Archimedean Valuation
- Archimedes Algorithm
- Archimedes' Axiom
- Archimedes' Cattle Problem
- Archimedes' Circles
- Archimedes' Constant
- Archimedes' Hat-Box Theorem