Try this;

rule "Combine ODMAnswers"

    when
        $a1:ODMAnswer( some check )
        $a2:ODMAnswer( assuming something making this one different than $a1 )


        eval(odmList contains $a1 && odmList contains $a2)
    then
        ODMAnswer answer = new ODMAnswer(  );
        odmList.add(answer);
        odmList.remove($a1);
        odmList.remove($a2);
end


On Wed, Jan 16, 2013 at 10:41 AM, Bojan Janisch <bojan.janisch@scai.fraunhofer.de> wrote:
rule "Combine ODMAnswers"

    when
        $a1:ODMAnswer(  )
        $a2:ODMAnswer(  )

        eval(odmList contains $a1 && odmList contains $a2)
    then
        ODMAnswer answer = new ODMAnswer(  );
        odmList.add(answer);
        odmList.remove($a1);
        odmList.remove($a2);
end