A woman and boy sit on a police motorcycle.
A woman and boy on a bicycle.
A police motorcycle and a bicycle are different vehicles
exists e1 x1 x2 x3 x4 x5.(on(e1,x4) & n_motorcycle(x4) & of(x4,x5) & n_police(x5) & Actor(e1,x1) & v_sit(e1) & n_boy(x3) & n_woman(x2) & subset_of(x3,x1) & subset_of(x2,x1))
exists s1 x1 x2 x3.(a_topic(s1) & subset_of(x2,s1) & on(x2,x3) & n_bicycle(x3) & n_boy(x2) & subset_of(x1,s1) & n_woman(x1))