proposition: Lemma Exercise4_8h: order_on E48Io E48I.
proof: Proof. hnf;move: (Ninto_wor \0c \1c)=> [[ok _] ->]. split => //;set_extens t. move /(NintcP NS1) => t1. case: (equal_or_not t \1c) => to; first by apply /set2_P; right. by move /clt1: (conj t1 to) => -> ; apply /set2_P; left. case /set2_P => ->; apply /(NintcP NS1); fprops; apply:cle_01. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)