Has anybody ever seen a situation where a couple of patterns such as

   Fact( field >= 10 )
   not Fact( field > 20 )

was appropriate? This does not match Facts where field isn't between 10 and 20, and so it would seem to be the same as

   Fact( field >= 10 && <= 20 )

but actually it doesn't match any such Fact whenever any other Fact with field > 20 is around.

Cheers
Wolfgang