  ss(system,shop_alarm,[active(shop_alarm)]),
     ss(valuable_item,diamond,[protected(diamond),protected_by(diamond,pressure_pad)]),
     ss(valuable_item,gold,[protected(gold),protected_by(gold,motion_detector)]),
     ss(valuable_item,artifact,[protected(artifact),protected_by(artifact,trip_wire)]),
     ss(guard,bert,[working(bert,shop_alarm)]),
     ss(burglar,tom,[casing_joint(tom),expertise(tom,none)]),
     ss(burglar,harry,[casing_joint(harry),expertise(harry,none)]),
     ss(burglar,dick,[casing_j