n = 4, thus |x| = 4
Definition: Let x be a string over S.
The length of x, |x|, is defined as follows:
1) if x = e, then |x| = 0
2) if x = a1…an, then |x| = n  
    for some n ³ 1, and ai Î S for all i = 1,…,n
Note: The length of x is the number of all symbols in x.
Example: Consider x =1010
Task: |x|
x = 1 0 1 0
a1a2a3a4
Length of String
 Gist: |a1a2…an| = n
4/20