Let $X$ be a D11: Set.
An D5134: Unsigned basic binary operation $d : X \times X \to [0, \infty]$ is a semimetric on $X$ if and only if

(1)	$\forall \, x, y, z \in X : d(x, z) \leq d(x, y) + d(y, z)$
(2)	$\forall \, x, y \in X : d(x, y) = d(y, x)$	(D3490: Symmetric function)
(3)	\begin{equation} \forall \, x, y \in X : d(x, y) = 0 \end{equation}