if something is used for something else, then that something else is the student of that something
everything is one_thing. else is river. used_thing is not artifact. used_thing is artifact. change is when_one_thing_becomes_another_thing. space is what_between_else. space is not what_between_else. change is not when_one_thing_becomes_another_thing. thing is substance. everything is not one_thing.