A man is servicing a truck.
A man is servicing.
in both sentences, a man is servicing.
exists e1 x1 x2.(Theme(e1,x2) & Actor(e1,x1) & v_service(e1) & n_truck(x2) & n_man(x1))
exists e1 x1.(Actor(e1,x1) & v_service(e1) & n_man(x1))