Addition theorem

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for weights

If a Hausdorff compactum can be represented as the union over a set of infinite cardinality of its subspaces of weight , then the weight of does not exceed . The addition theorem (which was formulated as a problem in [1]) was established in [3] for and in [4] in complete generality. Cf. Weight of a topological space.


[1] P.S. Aleksandrov, P. Urysohn, "Mémoire sur les espaces topologiques compacts" , Koninkl. Nederl. Akad. Wetensch. , Amsterdam (1929)
[2] R. Engelking, "General topology" , PWN (1977) (Translated from Polish)
[3] Yu.M. Smirnov, "On metrizability of bicompacta, decomposable as a sum of sets with a countable base" Fund. Math. , 43 (1956) pp. 387–393 (In Russian)
[4] A.V. Arkhangel'skii, "An addition theorem for weights of sets lying in bicompacta" Dokl. Akad. Nauk SSSR , 126 : 2 (1959) pp. 239–241 (In Russian)
[5] A.V. Arkhangel'skii, V.I. Ponomarev, "Fundamentals of general topology: problems and exercises" , Reidel (1984) (Translated from Russian)
How to Cite This Entry:
Addition theorem. Encyclopedia of Mathematics. URL:
This article was adapted from an original article by A.V. Arkhangel'skii (originator), which appeared in Encyclopedia of Mathematics - ISBN 1402006098. See original article