fact: Definition rec2down n := if n is n'.+1 then (loop2 n' 2 a0 a1 [:: a1; a0]) else [:: a0].
imports: Coq(ZArith Rfunctions NaryFunctions Lia) mathcomp.ssreflect(ssreflect ssrbool ssrfun eqtype ssrnat seq fintype bigop tuple) MathComp