O
- Odd number theorem (physics)
- Open mapping theorem (complex analysis)
- Open mapping theorem (functional analysis)
- Optical equivalence theorem (quantum optics) (quantum physics)
- Optional stopping theorem (probability theory)
- Orbit theorem (control theory)
- Orbit-stabilizer theorem (group theory)
- Ore's theorem (graph theory)
- Ornstein theorem (ergodic theory)
- Ortsbogen theorem (Euclidean geometry)
- Oseledec theorem (ergodic theory)
- Osterwalder–Schrader theorem (physics)
- Ostrowski's theorem (number theory)
- Ostrowski–Hadamard gap theorem (complex analysis)
Read more about this topic: List Of Theorems