proposition: Lemma formE r k (f : form k r) : untag f = k \+ r.
proof: Proof. by case: f=>[[j]] /=; rewrite /form_axiom /= => ->. Qed.
imports: mathcomp(ssreflect ssrbool ssrnat eqtype seq ssrfun) pcm(options axioms pred prelude) pcm(pcm autopcm unionmap heap) htt(model)