The set of all nonempty strings over an alphabet ![](eqns/e-2.gif) is denoted by ![](eqns/e-20.gif) . That is,
![](eqns/e-24.gif)
Note that is infinite. It contains no infinite strings but strings of arbitrary lengths. Reversal :
For any string the reversal of the string is . An inductive definition of reversal can be given as follows:
Languages :
A language over an alphabet is a set of strings over that alphabet. Therefore, a language L is any subset of . That is, any is a language. |