Weight of a topological space

2020 Mathematics Subject Classification: Primary: 54A25 [MSN][ZBL]

The smallest cardinal number which is the cardinality of an open base of a topological space. The weight, together with the cardinality, is the most important cardinal invariant of a topological space.

A space satisfies the second axiom of countability if and only if it has countable weight.

#### References[edit]

[a1] |  A.V. Arkhangel'skii, "Topological function spaces" , Kluwer (1991) (Translated from Russian)

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[a2] |  I. Juhász, "Cardinal functions in topology" , North-Holland (1971)
[a3] |  Mary Ellen Rudin, Lectures on Set Theoretic Topology, American Mathematical Society (1975) ISBN 0-8218-1673-X Zbl 0318.54001