proposition: Lemma Exercise1_22m: open_r r emptyset.
proof: Proof. split. split;[fprops | by move=> x y /in_set0]. move => v [sv ov] [_ ]; rewrite iorder_sr // => h;symmetry;apply /set0_P. by move=> y yv; move: (h _ yv) => [z /in_set0]. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)