A guy on a bmx bike.
A man on a bike.
he is a guy so he must be a man.
exists x1 x2 x3.(a_topic(x1) & on(x1,x2) & n_bike(x2) & of(x2,x3) & n_bmx(x3) & n_guy(x1))
exists x1 x2.(a_topic(x1) & on(x1,x2) & n_bike(x2) & n_man(x1))