proposition: Lemma entourage_ball {R : numDomainType} (M : pseudoMetricType R) (e : {posnum R}) : entourage [set xy : M * M | ball xy.1 e%:num xy.2].
proof: Proof. by rewrite -entourage_ballE; exists e%:num => /=. Qed.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap generic_quotient) mathcomp(boolp classical_sets functions) mathcomp(cardinality mathcomp_extra fsbigop) reals signed