fact: Definition fusc_prop f:= [/\ f \0c = \0c, f \1c = \1c, (forall n, natp n -> f (cdouble n) = f n) & (forall n, natp n -> f (csucc (cdouble n)) = f n +c f (csucc n)) ].
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)