proposition: Lemma cexit2 h1 h : h1 = Unit -> h1 \+ h = h.
proof: Proof. by move=>->; rewrite unitL. Qed.
imports: mathcomp(ssreflect ssrbool ssrnat eqtype seq ssrfun) pcm(options axioms pred prelude) pcm(pcm autopcm unionmap heap) htt(model)