# Obtain a grammar for the language (i) L = {a ^m b ^n ; m ≠ n ; m , n > 0 }

Obtain a grammar for the language

• $L = \{a^m b^n \mid m ≠ n , m > 0 , n > 0 \}$.

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If this is homework, it should be homework-tagged. BTW What have you tried? –  dtldarek Aug 8 '13 at 9:23

Hint:

• Let $L_0 = \{a^nb^n \mid n > 0\}$.
• Let $L_1 = \{a^k \mid k > 0\} \circ L_0$ and $L_2 = L_0 \circ \{b^k \mid k > 0\}$.
• Then $L = L_1 \cup L_2$.

I hope this helps $\ddot\smile$

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You want $L_2=L_0 \circ\{b^k\mid k>0\}$. –  Rick Decker Aug 8 '13 at 14:07
@RickDecker Yeah, thanks. –  dtldarek Aug 8 '13 at 14:25
Since $m\neq n$, there are two situations: $m > n$ or $m < n$. Each case can be treated seperately. In the first case, each word must contain $aab$, since $m,n>0$. So start with the string $aab$, and in each step add either both an $a$ and a $b$, or just add an $a$. This information is all you need, so try writing the productions by yourself.