proposition: Lemma add_N1_Zp p (x : 'Z_p) : -1 + x = ord_pred x.
proof: Proof. by rewrite addrC sub_Zp_1. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool choice eqtype ssrnat seq div) mathcomp(fintype bigop finset prime fingroup) mathcomp(ssralg finalg countalg)