Definition: Let x be a string over S.
The reversal of x, reversal(x), is defined as:
1) if x = e then reversal(e) = e
2) if x = a1…an then reversal(a1…an) = an…a1
    for some n ³ 1, and ai Î S for all i = 1,…,n
Example: Consider x =1010
Task: reversal(x)
reversal(           ) =             , so
a1
a1
a2
a2
a3
a3
a4
a4
reversal(           ) =            
1
1
0
0
1
1
0
0
Reversal of String
 Gist: reversal(a1…an) = an…a1
7/20