A man sits on a motorcycle and a woman is on the back.
a man is not riding anything
He can either be on a motorcycle or not riding anything, but not both.
exists e1 p1 x1 x2 x3 x4.(n_back(x4) & on(x3,x4) & n_woman(x3) & on(e1,x2) & n_motorcycle(x2) & Actor(e1,x1) & v_sit(e1) & n_man(x1))
exists x1.(-all x2.(n_thing(x2) -> exists e1.(Theme(e1,x2) & Actor(e1,x1) & v_ride(e1))) & n_man(x1))