proposition: Lemma valid_fresh h v t : fresh h <= t -> valid (t \-> v \+ h) = valid h.
proof: Proof. by move=>N; rewrite validPtUn /= (fresh0N N) (ordfresh_dom N) andbT. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path interval) pcm(options prelude pred finmap rtc seqext useqord uslice uconsec)