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Results tagged with context-free
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user 111799
Questions about the set of languages (equivalently) described by context-free grammars or accepted by (non-deterministic) pushdown automata.
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Variable derives itself
In Sipser's Introduction to the theory of computation (3rd edition), I found the following claim.
Consider the grammar:
$$
\begin{align*}
&R \to XRX \mid S \\
&S \to aTb \mid bTa \\
&T \to XTX \mid …
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