fact: Fixpoint fib_pure n := if n is n'.+1 then if n' is n''.+1 then fib_pure n' + fib_pure n'' else 1 else 0.
imports: mathcomp(ssreflect ssrbool ssrnat eqtype seq ssrfun) fcsl(prelude pred pcm unionmap heap) HTT(stmod stsep stlog stlogR)