Absolute Geometry
Geometry which depends only on the first four of Euclid's Postulates and not on the Parallel Postulate. Euclid 
himself used only the first four postulates for the first 28 propositions of the Elements">Elements, butwas forced to invoke the Parallel Postulate on the 29th.
References
Hofstadter, D. R. Gödel, Escher, Bach: An Eternal Golden Braid. New York: Vintage Books, pp. 90-91, 1989.
- Euler Formula
- 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