on(red_box, table).
on(glove, red_box).
on(blue_box, table).
on(baseball, blue_box).

##</code><code>##

?- on(X,Y),on(Y,Z).

##</code><code>##

gives(ovid,book(learning_perl,[merlyn,rootbeer],publisher(o_reilly),third_edition),grep).