chosky normal theorem

One of the simplest and most useful forms is called the Chomsky normal form. Chomsky normal form is useful in giving algorithms for working with context-free grammars.Any context-free language is generated by a context-free grammar in Chomsky normal form. We can convert any grammar G into Chomsky normal form. The conversion has several stages wherein rules that violate the conditions are replaced with equivalent ones that are satisfactory .
First, we add a new start variable. Then, we eliminate all epsilon rules of the form A -->e.We also eliminate
all unit rules of the form A ---+ B. In both cases we patch up the grammar to be sure that it still generates the same language. Finally, we convert the remaining rules into the proper form.
Greibach Normal Form is another useful form can be created from Grammar G which must be understanding two theorem:first theorem substitution theorem and second is left-recursive theorem
and how used them to convert CNF to GNF which include number of step
1-convert CFG to CNF
2-assignment variable to unit form A1, A2, A3 ......
3-if j if j=i used theorem left recursive
and continuous until form j>i
4-substitution theorem used when j>i after step 3