Definition:Infix Notation

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
 * $$s \mathcal{R} t$$.

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