Triplets

 A subscript triplet consists of three parts:  the first two parts
 designate a range of subscript values and the third part designates
 the increment (stride) between each value.  It takes the following
 form:

   [subscript-1] : [subscript-2] [:stride]

   subscript-1   Is a scalar numeric expression representing 
                 the first value in the subscript sequence.
                 If omitted, the declared lower bound of the 
                 dimension is used.

   subscript-2   Is a scalar numeric expression representing 
                 the last value in the subscript sequence.
                 If omitted, the declared upper bound of the 
                 dimension is used.

                 When indicating sections of an assumed-size 
                 array, this subscript must be specified.

   stride        Is a scalar numeric expression representing 
                 the increment between successive subscripts 
                 in the sequence.  It must have a nonzero value.
                 If it is omitted, it is assumed to be 1.

 The stride has the following effects:

  o  If the stride is positive, the subscript range starts with the
     first subscript and is incremented by the value of the stride,
     until the largest value less than or equal to the second
     subscript is attained.

     For example, if an array has been declared as B(6,3,2), the
     array section specified as B(2:4,1:2,2) is a rank-two array
     with shape (3,2) and size 6.  It consists of the following six
     elements:

         B(2,1,2)   B(2,2,2)
         B(3,1,2)   B(3,2,2)
         B(4,1,2)   B(4,2,2)

     If the first subscript is greater than the second subscript,
     the range is empty.

  o  If the stride is negative, the subscript range starts with the
     value of the first subscript and is decremented by the absolute
     value of the stride, until the smallest value greater than or
     equal to the second subscript is attained.

     For example, if an array has been declared as A(15), the array
     section specified as A(10:3:-2) is a rank-one array with shape
     (4) and size 4.  It consists of the following four elements:

         A(10)
         A(8)
         A(6)
         A(4)

     If the second subscript is greater than the first subscript,
     the range is empty.


 If a range specified by the stride is empty, the array section has
 a size of zero.

 A subscript in a subscript triplet need not be within the declared
 bounds for that dimension if all values used to select the array
 elements are within the declared bounds.  For example, if an array
 has been declared as A(15), the array section specified as
 A(4:16:10) is valid.  The section is a rank-one array with shape
 (2) and size 2.  It consists of elements A(4) and A(14).

 If the subscript triplet does not specify bounds or stride, but
 only a colon (:), the entire declared range for the dimension is
 used.