fact: Definition elems_ {A : Type} (def : A) (l : list A) := let n := length l in bind (choose (0, n - 1)) (fun n' => ret (List.nth n' l def)).
imports: ZArith List Lia mathcomp.ssreflect.ssreflect mathcomp(ssrfun ssrbool ssrnat seq eqtype) QuickChick(Sets Tactics RandomQC)