A guy on a bmx bike.
A man is walking with his dog.
The guy can't be on a bmx bike and be walking his dog at the same time.
exists x1 x2 x3.(a_topic(x1) & on(x1,x2) & n_bike(x2) & of(x2,x3) & n_bmx(x3) & n_guy(x1))
exists e1 x1 x2.(with(e1,x2) & n_dog(x2) & of(x2,x1) & n_male(x1) & Actor(e1,x1) & v_walk(e1) & n_man(x1))