Children on tricycles.
The tricycles have children on them.
If children are on a tricycle then the tricycle have children on them.
exists x1 x2.(a_topic(x1) & on(x1,x2) & n_tricycle(x2) & n_child(x1))
exists e1 x1 x2.(n_thing(x1) & n_tricycle(x1) & on(e1,x1) & Theme(e1,x2) & Actor(e1,x1) & v_have(e1) & n_child(x2))