proposition: Lemma BZm_hi_pr x: inc x BZm -> BZm_of_nat (BZ_val x) = x.
proof: Proof. rewrite /BZm_of_nat;case /setU1_P. by move /indexed_P => [pa] /setC1_P [pb pc] pd; Ytac0; rewrite -{2} pa pd. by move => ->; rewrite BZ0_val; Ytac0. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)