Result grammar is different from the original

[VascoRato]

I gave it the simple grammar:

S -> A A | B
A -> a | ϵ
B -> b

The resulting grammar was the following:

S -> A A
   | b
A -> a
B -> b

On the original grammar, the word a was valid. On the result CNF, it is not. The CNF does not define the same language as the original CFG.

[CyberZHG]

Thanks. The result now becomes:

S -> A A
   | ϵ
   | b
   | a
A -> a