Hahn-Banach Theorem
A linear Functional defined on a Subspace of a Vector Space 
and which is dominated by a sublinear function defined on has a linear extension which is also dominated by the sublinear function.
References
Zeidler, E. Applied Functional Analysis: Applications to Mathematical Physics. New York: Springer-Verlag, 1995.
- Compact Surface
- Companion Knot
- Comparability Graph
- Comparison Test
- Compass
- Compatible
- Complementary Angle
- Complement Graph
- Complement Knot
- Complement Set
- Complete
- Complete Axiomatic Theory
- Complete Bigraph
- Complete Bipartite Graph
- Complete Functions
- Complete Graph
- Complete k-Partite Graph
- Completely Regular Graph
- Complete Metric Space
- Completeness Property
- Complete Permutation
- Complete Quadrangle
- Complete Quadrilateral
- Complete Residue System
- Complete Sequence