Editing Sequitur algorithm (section)

=== Rule utility ===
This constraint ensures that all the rules are used more than once in the right sides of all the productions of the grammar, i.e., if a rule occurs just once, it should be removed from the grammar and its occurrence should be substituted with the symbols from which it is created. For example, in the above example, if one scans the last symbol and applies digram uniqueness for 'Aa', then the grammar will produce: '''S→BB, A→ab, B→Aa'''. Now, rule 'A' occurs only once in the grammar in '''B→Aa'''. Therefore, A is deleted and finally the grammar becomes
: '''S→BB, B→aba'''.
This constraint helps reduce the number of rules in the grammar.