proposition: Lemma BZdvdorder_sr: substrate BZdvdorder = BZps.
proof: Proof. rewrite /BZdvdorder graph_on_sr //. by move => a /BZps_iP [ap anz]; move: (BZdvd_itself (BZp_sBZ ap) anz)=> []. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)