>So explain the rule so it's simple. DNA is only 4 base pairs and they only connect 1:1 yet the diversity is incredible. Lego also is simple, yet the possibility to construct is only limited by imaginiation. Hardly dumbed down.
>

Hi Mike,

That may not be possible. What seems simple for one person may seem very complex or even impossible to understand for another.

In order for an index to be used for a Rushmore optimization, an index expression should match an expression in WHERE. The word match doesn't mean that the text of the expressions, as they are written, has to be exactly the same or their byte code has to be exactly the same. It rather means that the result of executing both expressions for the same record is the same. To perform the comparison, VFP uses complex routine that ignores insignificant differences between expressions - the differences that do not cause differences in results.

In some scenarios, there may be other requirements that also should be met. For example, collate sequence of the index should match current collate sequence, table's code page should match current code page, etc.

I've tried to explain the rule, it is up to you to decide whether it is a simple rule.

Thanks,
Aleksey.