inverse
Given a {function}, f : D -> C, a function g : C
-> D is called a left inverse for f if for all d in D, g (f d)
◦ d and a right inverse if, for all c in C, f (g c) ◦ c and an
inverse if both conditions hold. Only an {injection} has a
left inverse, only a {surjection} has a right inverse and only
a {bijection} has inverses. The inverse of f is often written
as f with a -1 superscript.
(1996-03-12)