\begin{definition}[Definition:Parsing Sequence]
Let $\FF$ be a formal language with alphabet $\AA$.
Let $S$ be a collation in $\AA$.
A '''parsing sequence''' for $S$ in $\FF$ is a sequence of collations in $\FF$ formed by application of rules of formation of $\FF$ from previous collations in this sequence, and ending in the collation $S$.
If $S$ has no '''parsing sequence''' in $\FF$, then it is not a well-formed formula in $\FF$.
A parsing sequence for a given well-formed formula in any formal language is usually not unique.
Thus, we can determine whether $S$ is a well-formed formula in any formal language by using a sequence of rules of formation of that language.
To '''parse''' a collation in a formal language is to find a parsing sequence for that collation, and thereby to determine whether or not it is a well-formed formula.
\end{definition}