On 1 June 2011 16:55, Simon Chen <simonchennj(a)gmail.com&gt; wrote: In this particular case you might try rule "test3" when Number3($a: a, $b: b, $c) not Number3( a == $a, b == $b, c < $c ) then System.out.println($a + " " + $b + " " + $c); end Event this will fail, if there are two identical (w.r.t. a, b and c) Number3 objects. For the general case, you must have some way of picking a single Number3 with some a/b-combination. Alternatively, insert possibly multiple triplets <a,b,min(c)> and harvest one from each group, using additional rules. Or use an additional fact containing <a,b(,c)> to indicate that you have computed the minimum. But then you must get rid of these auxiliaries. -W