# Lindelöf number

From Encyclopedia of Mathematics

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2010 Mathematics Subject Classification: *Primary:* 54A25 [MSN][ZBL]

*density character*

One of the cardinal characteristics of a topological space. The least infinite cardinal number $\tau$ such that every open covering has a subcovering of cardinality at most $\tau$.

#### References

- Mary Ellen Rudin,
*Lectures on Set Theoretic Topology*, American Mathematical Society (1975) ISBN 0-8218-1673-X

**How to Cite This Entry:**

Lindelöf number.

*Encyclopedia of Mathematics.*URL: http://encyclopediaofmath.org/index.php?title=Lindel%C3%B6f_number&oldid=35345