(=> (instance ?GROUP AgeGroup) (forall (?MEMB1 ?MEMB2 ?AGE1 ?AGE2) (=> (and (member ?MEMB1 ?GROUP) (member ?MEMB2 ?GROUP) (age ?MEMB1 ?AGE1) (age ?MEMB2 ?AGE2)) (equal ?AGE1 ?AGE2))))