proposition: Lemma size_domPtUn k v f : valid (pts k v \+ f) -> size (dom (pts k v \+ f)) = 1 + size (dom f).
proof: Proof. by move=>W; rewrite size_domUn // domPtK (validPtUn_cond W). Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path bigop) pcm(options prelude finmap seqperm pred seqext) pcm(pcm morphism)