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Regular expressions consist of regular operations such as:
- OR (|)
- AND (&)
- concatenation
- Kleene star (*)
The alphabet for the regular expressions are arbitrary tuples of integers. One may define regular expressions on an alphabet of 0-9, but can also specify, for example, [1, -1, 1][0, 1, -1]* to mean 10* in the first coordinate, -11* in the second, and 1-1* in the third. In particular, one can specify numbers above 9 and below 0, provided brackets are used (e.g. 1[10]* is 1 followed by an arbitrary number of 10s and similar for 1[-1]*).
Brackets may also be used for numbers 0-9 (e.g. [1][10]*) but are not mandatory in this case. A number system or alphabet must be supplied for each coordinate in the expression's tuples.