proposition: Lemma subst_term_poly_var_var {P} : subst_term poly_var var P = P.
proof: Proof. by apply: idSubst_term. Qed.
imports: List Lia Undecidability.SystemF.SysF Undecidability.SystemF.Autosubst.syntax Undecidability.SystemF.Autosubst.unscoped Undecidability.SystemF.Util(Facts poly_type_facts pure_term_facts) ssreflect ssrbool ssrfun