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# Mathematics Encyclopedia

# O

O-group

Oberbeck-Boussinesq equations

Oblique derivative

Obstacle scattering

Octacode

Octahedral space

Odd function

Odd number

Odlyzko bounds

Olevskii transform

Omega-completeness

Omega-squared distribution

O'Nan-Scott theorem

One-dimensional manifold

One-factor

One-factorization

One-parameter semi-group

Open-closed set

Open manifold

Open mapping theorem (complex analysis)

Open book decomposition

Open set

Operational calculus

Operations research

Operator colligation

Operator-irreducible representation

Operator ring

Operator topology

Operator vessel

Opposite algebra

Optimal control

Optimal programming control

Optimal quadrature

Orbit stability Order

Order on a set

Ordered group

Ordered groupoid

Ordered ring

Ordered semi-group

Ordinal power

Ordinary differential equation

Orientation

Orlicz-Lorentz space

Orlicz-Sobolev space

Orlicz class

Orlicz space

Orlicz–Lorentz space

Orlicz–Sobolev space

Ornstein-Chacon ergodic theorem

Orr-Sommerfeld equation

Orthogonal Latin squares