duality

名词 duality:

1. being twofold; a classification into two opposed parts or subclasses
   同义词：dichotomy
2. (physics) the property of matter and electromagnetic radiation that is characterized by the fact that some properties can be explained best by wave theory and others by particle theory
   同义词：wave-particle duality
3. (geometry) the interchangeability of the roles of points and planes in the theorems of projective geometry