Papyrus 95

Template:Multiple issues In computer science, a counter automaton is a Pushdown automaton with only two symbols, A and the initial symbol in $\Gamma \,$ (the finite set of stack symbols). This class of automata can recognize a subset of Context free languages, for instance the language:

$\{\ a^{n}b^{n}:n\in \mathbb {N} \}$

To accept the above language, let x be a word on the form above. The automaton can use the symbol A to count the number of a's in x (writing an A for each a in x) and deleting an A for each b in x.

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