Substrings

 A character substring is a contiguous segment of a character
 variable, character array element, or character field reference.
 It has one of the following forms:

    v([e1]:[e2])  
    a(s[,s]...)([e1]:[e2]) 

    v    Is a character variable name
    a    Is a character array name
    s    Is a subscript expression
    e1   Is a numeric expression specifying the leftmost
         character position of the substring
    e2   Is a numeric expression specifying the rightmost
         character position of the substring

 Both e1 and e2 must be within the range 1,2, ..., len, where len is
 the length of the parent character string.  If e1 exceeds e2, the
 substring has length zero.