proposition: Fact ren_poly_type_many_poly_abs {ξ n target} : ren_poly_type ξ (many_poly_abs n target) = many_poly_abs n (ren_poly_type (Nat.iter n up_ren ξ) target).
proof: Proof. elim: n ξ; first done. move=> n IH ξ /=. congr poly_abs. by rewrite IH iter_last. Qed.
imports: List Lia Undecidability.SystemF.SysF Undecidability.SystemF.Autosubst.syntax Undecidability.SystemF.Autosubst.unscoped Undecidability.SystemF.Util.Facts ssreflect ssrbool ssrfun