proposition: Fact subst_poly_type_poly_var {t} : subst_poly_type poly_var t = t.
proof: Proof. by rewrite idSubst_poly_type. Qed.
imports: List Lia Undecidability.SystemF.SysF Undecidability.SystemF.Autosubst.syntax Undecidability.SystemF.Autosubst.unscoped Undecidability.SystemF.Util.Facts ssreflect ssrbool ssrfun