twArComp( aArray, bComp, nStart, nStop )
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     Compares all elements of aArray using the bComp block from nStart
     to nStop (if specified, otherwise entire array) and returns the
     result.  Several sample blocks are provided in Array.ch.

     This function was taken from Nantucket Source File Array.prg.

       Arguments:

     aArray - 'A' Array to process.

     bComp  - 'B' Block with which to perform the compare.

     nStart - 'N' Start element. Defaults to 1.

     nStop  - 'N' Finish element. Defaults to last element.

       Return:

     Element Number which fits condition.

       Example:

     bLength := LEN( twArComp( Buttons,
                     {|x,y| LEN(x) > LEN(y)} ))

     Returns array element of Buttons[] whose length is a maximum.