A guy on a motorcycle at a streetlight.
A man wearing a white helmet sits on his motorcycle.
The guy on a motorcycle is not implied to be wearing a white helmet.
exists x1 x2 x3.(a_topic(x1) & on(x1,x2) & at(x2,x3) & n_streetlight(x3) & n_motorcycle(x2) & n_guy(x1))
exists e1 e2 s1 x1 x2 x3 x4.(on(e2,x4) & n_motorcycle(x4) & of(x4,x1) & n_male(x1) & Actor(e2,x1) & v_sit(e2) & Theme(e1,x3) & Actor(e1,x2) & v_wear(e1) & n_helmet(x3) & a_white(s1) & Theme(s1,x3) & (x1 = x2) & n_man(x1))