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I am trying to create a PDA with at most 7 states that accepts the following language over the alphabet $\Sigma = \{a,b\}$:

$$ \{a^{2k}b^{3k} \mid k \geq 0\} $$

The tricky part is that multiple push allowed but multiple pop is not allowed. I was able to find the easy solution when multi push/pop is allowed. I am looking for solutions where multi push/pop is not allowed and multi push is allowed but multi pop is not allowed.

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  • $\begingroup$ Multiple pop can be simulated by adding additional states to keep track of the pop-ed symbols. $\endgroup$
    – Steven
    May 15, 2022 at 18:11
  • $\begingroup$ For every second $a$ that you read, push $BBB$ into the stack. $\endgroup$
    – Yuval Filmus
    May 15, 2022 at 18:20
  • $\begingroup$ my stack alphabet is a single character, i tried to simulate k multi-pop by adding k additional state, i use epsilon transitions between these states and pop per each state. i guess it should work. thanks for the tip $\endgroup$
    – Utku Kalkanlı
    May 15, 2022 at 18:23
  • $\begingroup$ @YuvalFilmus exactly what i need thanks $\endgroup$
    – Utku Kalkanlı
    May 15, 2022 at 18:26

2 Answers 2

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For every second $a$ that you read, push $BBB$ into the stack.

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Here is another solution. For every $aa$ you could check every $bbb$(skips first $b$, keep stack's present top $a$ as it is and pop $2a$ against for last $2b$).

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