A classification into two subclasses or opposed parts. / (projective geometry) The interchangeability of points and planes.

plural of duality

(mathematics) Any of various kinds of duality found in representation theory of Lie algebras, abstract algebras, and topology.

plural of Koszul duality

(physics) The concept applying to all matter and radiation, but most evident in light and particles such as the electron, that properties of waves and of particles are exhibited simultaneously