Alexandroff
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For such spaces the Alexandroff extension is called the one-point compactification or Alexandroff compactification.
In this case it is called the one-point compactification or Alexandroff compactification of X. Recall from the above discussion that any compactification with one point remainder is necessarily (isomorphic to) the Alexandroff compactification.
Descriptive set theory, measure theory and analysis In 1916, Alexandroff and Hausdorff independently solved P. Alexandroff: Sur la puissance des ensembles mesurables B. Comptes rendus Acad.
In particular, homeomorphic spaces have isomorphic Alexandroff extensions.
The one-point compactification In particular, the Alexandroff extension is a compactification of X if and only if X is Hausdorff, noncompact and locally compact.
The theorem of Alexandroff and Hausdorff was a strong impetus for further development of descriptive set theory.