I forgot to mention another source that gives as exercise to prove that {a^n| with n a square} is not recognizable as a language by a pushdown automaton.

You might be right about Perl regexes being more powerful. I honestly don't know so I'll call it a day.

In reply to Re^2: check for square-number with a regex by spx2
in thread check for square-number with a regex by Ratazong

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