proposition: Lemma Exercise4_8k: order_on E48AJIo E48AJI /\ order_on E48APIo E48API.
proof: Proof. have s1: sub (irreds r) (substrate r) by apply: Zo_S. by move: (Exercise4_8j s1) (Exercise4_8j Exercise4_7e) => [p1 p2][p3 p4]. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)