proposition: Lemma dom_inNRX k f1 f2 : valid (f1 \+ f2) -> k \in dom f2 -> ~ k \in dom f1.
proof: Proof. by move=>W /(dom_inNR W)/negbTE ->. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path bigop) pcm(options prelude finmap seqperm pred seqext) pcm(pcm morphism)