Ultrafilters on Balleans
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- Protasov, I.V. & Slobodianiuk, S.V. Ukr Math J (2016) 67: 1922. doi:10.1007/s11253-016-1200-y
A ballean (or, equivalently, a coarse structure) is an asymptotic counterpart of a uniform space. We introduce three ultrafilter satellites of a ballean (namely, corona, companion, and corona companion), estimate the basic cardinal invariants of the corona, and characterize the subsets of balleans in terms of companions.