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Chomsky Normal Form:

1. Add the rule S_0 -> S

2. Break long rules into smaller ones:

   if A -> s_1 ... s_n is a rule where n > 2, then delete it and
   instead add the rules

		A       -> s_1 Z_1
                Z_1     -> s_2 Z_2
		        .
		        .
		        .
                Z_{n-2} -> s_{n-1} s_n

   The Z's are new variables.

3. A variable is nullable if the empty string can be derived from it.

   Find out all nullable variables.

   For all rules of the form A -> \alpha \beta (i.e., those whose
   right-hand sides have length 2) do:
   {
    if \alpha is a nullable variable, add the rule A -> \beta

    if \beta is a nullable variable, add the rule A -> \alpha
   }

   Delete all epsilon-rules.

   Add S_0 -> e if S_0 is nullable.

4. For every unmarked unit rule A -> B do
   { 
     For every rule B -> u do
      { Add the rule A -> u };
     Mark A -> B for deletion;
   }

   Delete all unit rules.

5. Create new variables X_a for every symbol a in the alphabet
   and add the rules X_a -> a

   If a terminal symbol appears in the RHS of a rule, and this
   RHS has length = 2, then replace the occurrence with its
   corresponding (newly created) variable.