# Lindelöf number

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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