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Topologies generated by ideals

Carlos Uzcátegui (2006)

Commentationes Mathematicae Universitatis Carolinae

A topological space X is said to be generated by an ideal if for all A X and all x A ¯ there is E A in such that x E ¯ , and is said to be weakly generated by if whenever a subset A of X contains E ¯ for every E A with E , then A itself is closed. An important class of examples are the so called weakly discretely generated spaces (which include sequential, scattered and compact Hausdorff spaces). Another paradigmatic example is the class of Alexandroff spaces which corresponds to spaces generated by finite sets....

Topologies on groups determined by right cancellable ultrafilters

Igor V. Protasov (2009)

Commentationes Mathematicae Universitatis Carolinae

For every discrete group G , the Stone-Čech compactification β G of G has a natural structure of a compact right topological semigroup. An ultrafilter p G * , where G * = β G G , is called right cancellable if, given any q , r G * , q p = r p implies q = r . For every right cancellable ultrafilter p G * , we denote by G ( p ) the group G endowed with the strongest left invariant topology in which p converges to the identity of G . For any countable group G and any right cancellable ultrafilters p , q G * , we show that G ( p ) is homeomorphic to G ( q ) if and only if...

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