Foundations of Computing by Charles D. Allison

Author:Charles D. Allison
Language: eng
Format: mobi, epub, pdf
Publisher: leanpub.com
Published: 2019-12-11T16:00:00+00:00

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Example 6–7

To design a CFG for the language , we observe that for every generated there must also be an accompanying , but they can come in either or two orderings, and they don’t have to be adjacent. Consider the following CFG.

The first rule introduces the first, and conversely for the second. The symbol , being the start symbol, represents a string with an equal number of ’s and ’s. By inserting between the and and at the end of the replacement strings, we do not constrain how an acceptable string can be constructed. Let’s derive :

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