proposition: Lemma dom_NNL k f1 f2 : valid (f1 \+ f2) -> k \notin dom (f1 \+ f2) -> k \notin dom f1.
proof: Proof. by move=> D; apply/contra/dom_inIL. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path bigop) pcm(options prelude finmap seqperm pred seqext) pcm(pcm morphism)