fact: Fixpoint le s1 s2 := if s1 isn't x1 :: s1' then true else if s2 isn't x2 :: s2' then false else (x1 <= x2) && le s1' s2'.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)