proposition: Lemma entourage_split_ex (A : set (M * M)) : entourage A -> exists2 B, entourage B & B \; B `<=` A.
proof: Proof. exact: entourage_split_ex_subproof. Qed.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap generic_quotient) mathcomp(boolp classical_sets functions) mathcomp(cardinality mathcomp_extra fsbigop) reals signed