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Equality problem is checking if 2 DCFL's or CFL's are producing same language.

I read that it is decidable for DCFL and undecidable for CFL.

If we consider a DCFL like a^n b^2n / n>=1, here we can draw a PDA for this in two ways. So how can we check if 2 DCFL's produce the same language by just looking at the PDA as they are not unique?

Zephyr
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1 Answers1

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We can't. Infinitely many different PDAs for the same DCFL exist.

In 1997, Géraud Sénizergues proved that equivalence of DCFLs is decidable, and he was awarded the Gödel Prize for it.

For general context-free languages, it is undecidable. As a matter of fact, it is already undecidable for linear context-free languages.

reinierpost
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