Initial Graph Preprocessing

The next step is the preprocessing step. After observing that there are a subset of rules in the grammar that can be applied first, then ignored for the rest of the processing, a preprocessing grammar was made. This approach is not new, also being used by Anderson . The steps in the preprocessing grammar could be included in the main grammar, if desired, though possibly at the expense of parsing time.

The result of applying all the rules in the preprocessing grammar, which do basic categorisation of symbols and collect up multi-symbol items such as numbers, is shown in Figure (c).