>Rushmore only works when one side of the expression EXACTLY matches the index expression. Neither field1 or field2 match your index expression of field1>field2. If you have an index on field1 or on field2 then your expression would be optimizable. To optimize your index you would need something like (field1>field2) = .T.
Gee - All my effort and here's your answer in the next message 2 hours earlier :-)