In the second step, we introduce additional variables to get the first two
productions into normal form and we get the final result
Greibach Normal Form
Another useful grammatical form is the Greibach normal form. Here we put
restrictions not on the length of the right sides of a production, but on the
positions in which terminals and variables can appear. Arguments justifying
Greibach normal form are a little complicated and not very transparent.
Similarly, constructing a grammar in Greibach normal form equivalent to a given