Page "Limit cardinal" Paragraph 1

A cardinal λ is a strong limit cardinal if λ cannot be reached by repeated powerset operations.

This means that λ is nonzero and, for all κ < λ, 2 < sup > κ </ sup > < λ.

Every strong limit cardinal is also a weak limit cardinal, because κ < sup >+</ sup > ≤ 2 < sup > κ </ sup > for every cardinal κ, where κ < sup >+</ sup > denotes the successor cardinal of κ.