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Because the system assumes that the alphabet consists only of the symbols occurring in the input automaton, it may be safer to use the -difference option. In this case an automaton is written to standard output, defining all strings that are defined by the automaton in File1 except for the strings defined in File2. For example, if the file abc.nd consists of the automaton defining all strings over the alphabet {a,b,c}, then we get:
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The system also supports the construction of an automaton on the basis of a regular expression: the option -r Expression can be used. The operators that are allowed are Kleene closure (*), concatenation (.) and union (;). Moreover, it is possible to have transduction pairs (:). Finally, the system understands intervals. The expression a-z is a shorthand for the expression a;b;c;..;z. For example:
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