The first letter of the Hebrew alphabet: א

Also used with a subscript to represent the various orders of infinity.

(Set Theory:)

Aleph (), unadorned with subscripts, is the common symbol for the cardinality of the continuum.

20 = ℵ

With subscript , ℵ0 (aleph-null) is the cardinality of the integers. With successive (ordinal) subscripts, ℵz is the z'th cardinal after ℵ0. The Continuum Hypothesis (CH) is that ℵ = ℵ1.

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