The rules that use the category "<contact_rel>" are:
<contact_directive-flight_advisory> <contact_type-point_id_type_none> <contact_type-point_id_type_none> <contact_rel> <air_location>
<contact_directive-flight_advisory> <contact_type-point_id_type_none> <contact_type-point_id_type_none> <contact_rel> <air_location>
<contact_type-point_id_type_none> <contact_rel> <air_location>
<contact_directive-flight_advisory> <contact_type-point_id_type_none> <contact_type-point_id_type_none> <contact_rel> <air_location>
<contact_type-point_id_type_none> <contact_rel> <air_location>
<contact_directive-flight_advisory> <contact_type-point_id_type_none> <contact_type-point_id_type_none> <contact_rel> <air_location>