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