Inclusion-Exclusion Principle
If 
, ..., 
are finite sets, then
where
is the sum of the Cardinalities of the intersections of the sets taken 
at a time.- Plus Perfect Number
- Plus Sign
- Plutarch Numbers
- Plücker Characteristics
- Plücker Relations
- Plücker's Conoid
- Plücker's Equations
- Pochhammer Symbol
- Pocklington-Lehmer Test
- Pocklington's Criterion
- Pocklington's Theorem
- Poggendorff Illusion
- Pohlke's Theorem
- Poincaré-Birkhoff Fixed Point Theorem
- Poincaré Conjecture
- Poincaré Duality
- Poincaré Formula
- Poincaré-Fuchs-Klein Automorphic Function
- Poincaré Group
- Poincaré-Hopf Index Theorem
- Poincaré Hyperbolic Disk
- Poincaré Manifold
- Poincaré Metric
- Poincaré Separation Theorem
- Poincaré's Holomorphic Lemma