A man in a yellow shirt is sitting on a motorcycle.
The man is wearing a motorcycle helmet.
Just because a man is sitting on a motorcycle does not necessarily mean that he is wearing a motorcycle helmet.
exists e1 s1 x1 x2 x3.(on(e1,x3) & n_motorcycle(x3) & Actor(e1,x1) & v_sit(e1) & in(x1,x2) & n_shirt(x2) & a_yellow(s1) & Theme(s1,x2) & n_man(x1))
exists e1 x1 x2 x3.(n_man(x1) & Theme(e1,x2) & Actor(e1,x1) & v_wear(e1) & n_helmet(x2) & of(x2,x3) & n_motorcycle(x3))