!AIUnit >>
 ...
;

!GameUnit :: AIUnit >>
 ...
;

!HasWings >> 
 ...         
;            

+FlyingMonster : GameUnit, HasWings >> 
 GameUnit, HasWings : _
 ...                                   
;                                      

Helicopter = FlyingMonster [Air]
MetalMarine = FlyingMonster [Sea]