proposition: Lemma equal_refl: forall x, equal x x.
proof: Proof. induction x; constructor; assumption. Qed.
imports: ATBR(Common) ATBR(Classes) ATBR(Graph) ATBR(SemiLattice) ATBR(SemiRing) ATBR(KleeneAlgebra) ATBR(MxGraph) ATBR(Reification)