Trivial
According to the Nobel Prize-winning physicist Richard Feynman 
(1985), mathematicians designate anyTheorem as ``trivial'' once a proof has been obtained--no matter how difficult the theorem was to prove in thefirst place. There are therefore exactly two types of true mathematical propositions: trivial ones, and those which have notyet been proven.
References
Feynman, R. P. and Leighton, R. Surely You're Joking, Mr. Feynman! New York: Bantam Books, 1985.
- Euler Four-Square Identity
- Euler Graph
- Eulerian Circuit
- Eulerian Cycle
- Eulerian Integral of the First Kind
- Eulerian Integral of the Second Kind
- Eulerian Number
- Eulerian Trail
- Euler Identity
- Euler Integral
- Euler-Jacobi Pseudoprime
- Euler-Lagrange Derivative
- Euler-Lagrange Differential Equation
- Euler L-Function
- Euler Line
- Euler-Lucas Pseudoprime
- Euler-Maclaurin Integration Formulas
- Euler-Mascheroni Constant
- Euler-Mascheroni Integrals
- Euler Measure
- Euler Number
- Euler Parameters
- Euler-Poincaré Characteristic
- Euler Polyhedral Formula
- Euler Polynomial