proposition: Lemma validUnAEC f1 f2 : valid (f1 \+ f2) = [&& valid f1, valid f2 & all [predC dom f2] (dom f1)].
proof: Proof. by rewrite validUnAE all_predC_sym. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path bigop) pcm(options prelude finmap seqperm pred seqext) pcm(pcm morphism)