Protasov, Igor2019-04-042019-04-042019-04-011576-9402https://riunet.upv.es/handle/10251/118978[EN] A ballean (or coarse space) is a set endowed with a coarse structure. A ballean X is called normal if any two asymptotically disjoint subsets of X are asymptotically separated. We say that a ballean X is ultra-normal (extremely normal) if any two unbounded subsets of X are not asymptotically disjoint (every unbounded subset of X is large). Every maximal ballean is extremely normal and every extremely normal ballean is ultranormal, but the converse statements do not hold. A normal ballean is ultranormal if and only if the Higson′s corona of X is a singleton. A discrete ballean X is ultranormal if and only if X is maximal. We construct a series of concrete balleans with extremal properties.Reconocimiento - No comercial - Sin obra derivada (by-nc-nd)BalleanCoarse structureBornologyMaximal balleanUltranormal balleanExtremely normal balleanArtículo2019-04-0410.4995/agt.2019.11260Abierto1989-4147