proposition: Lemma asimpl_f_comp t s1 s2 : t[s1][s2] = t[s1 >> subst_term s2].
proof: Proof. apply subst_comp. Qed.
imports: Undecidability.FOL.Syntax(Core Facts) Coq.Classes.Init Relation_Definitions Coq.Classes.RelationClasses Coq.Classes.Morphisms Setoid