sentences: if something is used for something else, then that something else is the student of that something
docs: used_car is used_thing. thing is substance. used_thing is artifact. else is river. change is when_one_thing_becomes_another_thing. space is what_between_else. used_object_for_sale is used_thing. everything is one_thing. anything_else is film. thing is one_individual_item.