A child on a plastic sled.
The child is on another object.
A child is an object. A plastic sled is a different object. So the child is on another object.
exists e1 x1 x2 x3.(a_topic(x1) & on(x1,x2) & Theme(e1,x3) & v_sled(e1) & (x2 = x3) & n_plastic(x2) & n_child(x1))
exists p1 x1 x2.(n_object(x2) & n_child(x1) & exists x3.(on(x1,x3) & n_object(x3) & -(x3 = x2)))