A person in a helmet on a motorcycle
Nobody has a helmet
If one person is wearing a helmet there cannot be nobody wearing a helmet.
exists x1 x2 x3.(a_topic(x1) & in(x1,x2) & on(x2,x3) & n_motorcycle(x3) & n_helmet(x2) & n_person(x1))
-exists e1 x1 x2.(Theme(e1,x2) & Actor(e1,x1) & v_have(e1) & n_helmet(x2) & n_person(x1))