tw_NtxRec( nOrder, nPosition )
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     Determine the record number given the logical offset from the top
     of an index file of a given record in a database.

       Arguments:

     nOrder - 'N' Index order for the required index. May be a return
                  from INDEXORD( 0 ).

     nPosition - 'N' Logical offset of the record number to find.

       Return:

     Numeric indicating the record number of the record at offset
     nPosition.

       Example:

     nRecord := tw_NtxRec( INDEXORD( 0 ), 34 )