Definition:Infix Notation

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
 * $$s \mathcal R t$$.

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