Fundamental Lemma of Calculus of Variations
If
with Continuous second Partial Derivatives, then 
on the Open Interval
.- Pick's Formula
- Pick's Theorem
- Picone's Theorem
- Piecewise Circular Curve
- Pie Cutting
- Pigeonhole Principle
- Pi Heptomino
- Pillai's Conjecture
- Pilot Vector
- Pinching Theorem
- Pinch Point
- Pine Cone Number
- Piriform
- Pisot-Vijayaraghavan Constants
- Pistol
- Pitchfork Bifurcation
- Pivoting
- Pivot Theorem
- Pizza Theorem
- Place (Digit)
- Place (Field)
- Place (Game)
- Planar Bubble Problem
- Planar Distance
- Planar Graph