proposition: Lemma pts_undef k v : pts k v = undef :> U <-> ~~ C k.
proof: Proof. by rewrite -(validPt k v) invalidE. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path bigop) pcm(options prelude finmap seqperm pred seqext) pcm(pcm morphism)