fact: Definition oneOf_ {A : Type} (def: G A) (gs : list (G A)) : G A := bind (choose (0, length gs - 1)) (nth def gs).
imports: ZArith List Lia mathcomp.ssreflect.ssreflect mathcomp(ssrfun ssrbool ssrnat seq eqtype) QuickChick(Sets Tactics RandomQC)