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Alex Rivera
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I'm reading through the dragon book and trying to solve an exercise that is stated as follows Write regular definitions for the following languages: All strings of digits with no repeated digits. Hint: Try this problem first with a few digits, such as { 0, 1, 2 }. Despite having tried to solve it for hours, I can't imagine a solution, beside the extremely wordy d0 -> 0? d1 -> 1? d2 -> 2? d3 -> 3? d4 -> 4? d5 -> 5? d6 -> 6? d7 -> 7? d8 -> 8? d9 -> 9? d10 -> d0d1d2d3d4d5d6d7d8d9 | d0d1d2d3d4d5d6d7d9d8 | ... Hence having to write 10! alternatives in d10 . Since we shall write this regular definition, I doubt that this is a proper solution. Can you help me please?
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