fact: Fixpoint foldri (s : seq T) (i : nat) : R := match s with | [::] => z0 | x :: s' => f x i (foldri s' i.+1) end.
imports: Coq(Rdefinitions Raxioms RIneq Rbasic_fun) mathcomp.ssreflect(ssreflect ssrfun ssrbool eqtype ssrnat seq bigop) MathComp1or2