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.
- Pentagrammic Dipyramid
- Pentagrammic Prism
- Pentakaidecagon
- Pentakis Dodecahedron
- Pentalpha
- Pentangle
- Pentatope
- Pentatope Number
- Pentomino
- Percent
- Percentage Error
- Percolation Theory
- Percolation Threshold
- Perfect Box
- Perfect Cubic
- Perfect Cuboid
- Perfect Difference Set
- Perfect Digital Invariant
- Perfect Information
- Perfect Magic Cube
- Perfect Number
- Perfect Partition
- Perfect Proportion
- Perfect Rectangle
- Perfect Ruler