# Definition:Occurrence (Formal Systems)

This page is about occurrences of collations in the context of formal systems. For other uses, see Definition:Occurrence.

## Definition

Let $\mathcal F$ be a formal language.

Let $S, T$ be collations in the alphabet of $\mathcal F$.

Each place where $S$ appears in $T$ is called an occurrence of $S$ in $T$.

## Also known as

Some sources refer to this as an instance.