proposition: Lemma map_nth' {A B : Type} {f : A -> B} {l : list A} {d : B} {n : nat} (d' : A) : n < length l -> nth n (map f l) d = f (nth n l d').
proof: Proof. move=> ?. rewrite -[RHS]map_nth. apply: nth_indep. by rewrite map_length. Qed.
imports: Undecidability.IntersectionTypes.CD Undecidability.IntersectionTypes.Util.CD_facts Undecidability.StringRewriting.SSTS Undecidability.LambdaCalculus.Util.term_facts Relations List PeanoNat Lia ssreflect ssrfun