proposition: Lemma getf_catl f g k (kfg : k \in domf (f + g)) (kf : k \in domf f) : k \notin domf g -> (f + g).[kfg] = f.[kf].
proof: Proof. by move=> kNg; apply: Some_inj; rewrite Some_fnd fnd_cat (negPf kNg) in_fnd. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrnat eqtype ssrfun seq) mathcomp(choice path finset finfun fintype bigop)