Editing Chomsky normal form (section)

===UNIT: Eliminate unit rules===

A unit rule is a rule of the form 
:''A'' → ''B'', 
where ''A'', ''B'' are nonterminal symbols.
To remove it, for each rule 
:''B'' →  ''X''<sub>1</sub> ... ''X''<sub>''n''</sub>, 
where  ''X''<sub>1</sub> ... ''X''<sub>''n''</sub> is a string of nonterminals and terminals, add rule 
:''A'' →  ''X''<sub>1</sub> ... ''X''<sub>''n''</sub> 
unless this is a unit rule which has already been (or is being) removed. The skipping of nonterminal symbol ''B'' in the resulting grammar is possible due to ''B'' being a member of the unit closure of nonterminal symbol ''A''.<ref>{{Cite book |last=Allison |first=Charles D. |title=Foundations of Computing: An Accessible Introduction to Automata and Formal Languages |publisher=Fresh Sources, Inc. |year=2022 |isbn=9780578944173 |pages=176 |language=en}}</ref>