fact: Fixpoint changes (s : seq R) : nat := (if s is a :: q then (a * (head 0 q) < 0)%R + changes q else 0)%N.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice fintype order) mathcomp(binomial bigop ssralg poly ssrnum ssrint rat) mathcomp(polydiv polyorder path interval polyrcf)