Let $\mathbb{N}$ be the D225: Set of natural numbers such that

(1)	$E \subseteq \mathbb{N}$ is a D78: Subset

A D993: Real number $\alpha \in \mathbb{R}$ is the natural number set density of $E$ if and only if \begin{equation} \lim_{n \to \infty} \frac{|E \cap \{ 1, \dots, n \}|}{n} = \alpha \end{equation}