| Alphabets, Strings and Languages | ||
| Example : 0110, 11, 001 are three strings over the binary alphabet { 0, 1 } .
aab, abcb, b, cc are four strings over the alphabet { a, b, c }. It is not the case that a string over some alphabet should contain all the symbols from the alphabet. For example, the string cc over the alphabet { a, b, c } does not contain the symbols a and b. Hence, it is true that a string over an alphabet is also a string over any superset of that alphabet.
Length of a string : Example : | 011 | = 4, |11| = 2, | b | = 1 It is convenient to introduce a notation e for the empty string, which contains no symbols at all. The length of the empty string e is zero, i.e., | e | = 0. |
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