proposition: Lemma app_ass_trans@{X} : forall {T : Type@{X} } (a b c : list T), (a ++ b) ++ c = a ++ b ++ c.
proof: Proof. induction a; simpl. reflexivity. intros. destruct (IHa b c). reflexivity. Defined.
imports: Coq.Lists.List Coq.Arith.PeanoNat Relations RelationClasses ExtLib.Core.RelDec ExtLib.Data.SigT ExtLib.Data.Member ExtLib.Data.ListNth ExtLib.Data.Option ExtLib.Tactics Coq.Classes.Morphisms