In
mathematics, a
duality, generally speaking, translates concepts, theorems or mathematical structures into other concepts, theorems or structures, in a one-to-one fashion, often (but not always) by means of an
involution operation: if the dual of
A is
B, then the dual of
B is
A. Such involutions sometimes have
fixed points, so that the dual of
A is
A itself. For example,
Desargues' theorem is self-dual in this sense under the
standard duality in projective geometry.