Let $Z_1, Z_2, Z_3, \dots \in \text{Gaussian}(0, 1)$ each be a D211: Standard gaussian random real number such that

(i)	$Z_1, Z_2, Z_3, \dots$ is an D2713: Independent random collection

A D3161: Random real number $X \in \text{Random}(\mathbb{R})$ is a chi-squared random unsigned real number with parameter $N \in \{ 1, 2, 3, \ldots \}$ if and only if \begin{equation} X \overset{d}{=} \sum_{n = 1}^N Z^2_n \end{equation}