proposition: Lemma fdfe_inv_prop A i (x := fdfe_inv A i): fin_disj_fam A -> inc i (fdfer A) -> fdfe A x = i /\ inc x (unionb A).
proof: Proof. move => ha /Zo_hi hb. apply:(select_pr hb) => j k jz <- kz /esym kp. apply: (fin_disj_fam_prop6 ha jz kz kp). Qed.
imports: mathcomp(ssreflect ssrbool ssrfun eqtype)