proposition: Lemma opp_seq_p1 A: fin_disj_fam A -> fin_disj_fam (opp_seq A).
proof: Proof. rewrite /opp_seq; move =>[qa qb qc qd]; split. - fprops. - by aw. - move => i j; aw; move => iz jz; bw => //. move:(ZSo iz) (ZSo jz); rewrite /intp - qb => sa sb. by case:(qc _ _ sa sb); [ move/(BZopp_inj iz jz); left | right ]. - move => i; aw => iz; bw => //. apply:qd; rewrite qb; exact:(ZSo iz). Qed.
imports: mathcomp(ssreflect ssrbool ssrfun eqtype)