proposition: Lemma validUnHC f1 f2 : valid (f1 \+ f2) = [&& valid f1, valid f2 & ~~ has [mem dom f2] (dom f1)].
proof: Proof. by rewrite validUnHE has_sym. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path bigop) pcm(options prelude finmap seqperm pred seqext) pcm(pcm morphism)