Wrecked ambulance is being towed by a large truck.
Wrecked ambulance is not being towed
The wrecked ambulance is either towed by a large truck  or not being towed.
exists e2 e1 s1 x1 x2.(Actor(e2,x2) & n_truck(x2) & a_large(s1) & Theme(s1,x2) & Theme(e2,x1) & v_tow(e2) & n_ambulance(x1) & Theme(e1,x1) & v_wreck(e1))
exists e1 x1.(-exists e2.(Theme(e2,x1) & v_tow(e2)) & n_ambulance(x1) & Theme(e1,x1) & v_wreck(e1))