proposition: Lemma BZ_in_ideal1 a b: intp a -> intp b -> (inc a (BZ_ideal2 a b) /\ inc b (BZ_ideal2 a b)).
proof: Proof. move: ZS1 ZS0 => z1 z0. move => az bz; split; apply /Zo_P;split => //. by exists \1z,\0z; rewrite BZprod_0r BZprod_1r // BZsum_0r. by exists \0z, \1z; rewrite BZprod_0r BZprod_1r // BZsum_0l. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)