Schröder-Bernstein Theorem
The Schröder-Bernstein theorem for numbers states that if
then
For Sets, the theorem states that if there are Injections of the Set
into the Set 
and of into , then there is a Bijective correspondence between and (i.e., they are Equipollent).See also Bijection, Equipollent, Injection- Oscillation
- Oscillation Land
- Osculating Circle
- Osculating Curves
- Osculating Interpolation
- Osculating Plane
- Osculating Sphere
- Osedelec Theorem
- Ostrowski's Inequality
- Ostrowski's Theorem
- Otter's Tree Enumeration Constants
- Outdegree
- Outer Automorphism Group
- Outer Product
- Oval
- Oval of Descartes
- Ovals of Cassini
- Overlapping Resonance Method
- Oversampling
- Ovoid
- Paasche's Index
- Packing
- Packing Density
- p-adic Number
- Padovan Sequence