proposition: Lemma InUn x f1 f2 : x \In (f1 \+ f2) -> x \In f1 \/ x \In f2.
proof: Proof. move/In_find=>F; move/find_some: (F); rewrite domUn inE=>/andP [W D]. case/orP: D F=>D; first by rewrite findUnL // D=>/In_find; left. by rewrite findUnR // D=>/In_find; right. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path bigop) pcm(options prelude finmap seqperm pred seqext) pcm(pcm morphism)