proposition: Lemma partition_inc_unique1 i j y: inc i (source f) -> inc y (Vf f i) -> inc j (source f) -> inc y (Vf f j) -> i = j.
proof: Proof. rewrite (proj33 ff) => p1 p2 p3 p4. by rewrite -(cover_at_pr fpa p1 p2) - (cover_at_pr fpa p3 p4). Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)