-- learn some inheritance paths:
parent-type |trudy> => |cat>
parent-type |cat> => |feline>
parent-type |feline> => |mammal>
parent-type |mammal> => |animal>
parent-type |rex> => |dog>
parent-type |dog> => |canine>
parent-type |canine> => |mammal>
-- now find the inheritance path for trudy and rex:
inherit-path[parent-type] (|trudy> + |rex>)
|animal: mammal: feline: cat: trudy> + |animal: mammal: canine: dog: rex>