fact: Fixpoint merge_sort_rec ss s := if s is [:: x1, x2 & s'] then let s1 := if leT x1 x2 then [:: x1; x2] else [:: x2; x1] in merge_sort_rec (merge_sort_push s1 ss) s' else merge_sort_pop s ss.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq)