The ordinal-indexed hierarchy of infinite cardinals: ℵ₀ = |ℕ|, ℵ_{α+1} is the least cardinal > ℵ_α, and ℵ_λ = sup_{α<λ} ℵ_α for limits λ.
The ordinal-indexed hierarchy of infinite cardinals: ℵ₀ = |ℕ|, ℵ_{α+1} is the least cardinal > ℵ_α, and ℵ_λ = sup_{α<λ} ℵ_α for limits λ.