\begin{definition}[Definition:Formal Grammar]
Let $\LL$ be a formal language whose alphabet is $\AA$.
The '''formal grammar''' of $\LL$ comprises of rules of formation, which determine whether collations in $\AA$ belong to $\LL$ or not.
Roughly speaking, there are two types of '''formal grammar''': top-down grammar and bottom-up grammar.
\end{definition}