Definition:Infix Notation/Binary Relation

Definition
Let $\mathcal R \subseteq S \times T$ be a binary relation.

When $\left({s, t}\right) \in \mathcal R$, we can write either:
 * $\mathcal R \left({s, t}\right)$

or
 * $s \mathop {\mathcal R} t$

The notation $s \mathop {\mathcal R} t$ is known as infix notation.