Coincidence point
（重定向自Coincident point）
In mathematics, a coincidence point (or simply coincidence) of two mappings is a point in their common domain having the same image.
Formally, given two mappings
we say that a point x in X is a coincidence point of f and g if f(x) = g(x).
Coincidence theory (the study of coincidence points) is, in most settings, a generalization of fixed point theory, the study of points x with f(x) = x. Fixed point theory is the special case obtained from the above by letting X = Y and taking g to be the identity mapping.