fact: Fixpoint zipwith (s1 : seq T1) (s2 : seq T2) := if s1 is x1 :: s1' then if s2 is x2 :: s2' then f x1 x2 :: zipwith s1' s2' else [::] else [::].
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq ssralg) mathcomp(path choice fintype tuple finset bigop poly matrix mxpoly) CoqEAL(hrel param refinements trivial_seq)