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I'm in a Formal languages class and have a grammar quiz coming up. I'm assuming something like this will appear.

Consider the alphabet $\Sigma$ = {a, b, c}. Construct a grammar that generates the language $L = \{bab^nabc^na^p \mid n ≥ 0, p ≥ 1\}$. Assume that the start variable is $S$.

Ran G.
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Terry Light
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  • and the problem is...? if there is no restriction on the grammar, there are many possible solution; I assume you meant a context-free grammar. – Ran G. Aug 31 '15 at 04:50
  • What research have you done? What have you tried? Have you tried using the techniques in http://cs.stackexchange.com/q/18524/755? This question looks like it is answered by the answers there. – D.W. Aug 31 '15 at 06:21

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One possible grammar is: $G = (N, \Sigma, P, S)$, where

$N = \{S,U,V\}$

$\Sigma = \{a,b,c\}$

$P = \{ S \to baUV, U \to ab|bUc, V \to a|aV \}$

The key observation here is breaking $bab^nabc^na^p$ into 3 parts, $ba$, $b^nabc^n$, and $a^p$, one fixed, one growing bidirectionally, and one simple repeatition. Express the growing patterns first, then merge them along with the fixed parts.

Terence Hang
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