fact: Definition backtrack {A : Type} (gs : list (nat * G (option A))) : G (option A) := backtrackFuel (length gs) (sum_fst gs) gs.
imports: Coq(String List ZArith Lia) mathcomp.ssreflect.ssreflect mathcomp(ssrfun ssrbool ssrnat eqtype seq) QuickChick(RandomQC RoseTrees Sets Tactics Producer)