Aleph number

In the branch of mathematics known as set theory, the aleph numbers are a sequence of numbers used to represent the cardinality (or size) of infinite sets. They are named after the symbol used to denote them, the Hebrew letter aleph ().The cardinality of the natural numbers is (aleph-null, also aleph-naught or aleph-zero) the next larger cardinality is aleph-one , then and so on. Continuing in this manner, it is possible to define a cardinal number  for every ordinal number α, as described below.The concept goes back to Georg Cantor, who defined the notion of cardinality and realized that infinite sets can have different cardinalities.
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