proposition: Lemma Exercise1_22t: least (reg_open_order r) (emptyset).
proof: Proof. move: (Exercise1_22m) => so. split; first by apply /Exercise1_22s1P. move=> x => /Exercise1_22s1P ox; apply /Exercise1_22rP;split;fprops. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)