A person on a tricycle.
The person is doing tricks on the tricycle.
Not all people are doing tricks when they are on a tricycle.
exists x1 x2.(a_topic(x1) & on(x1,x2) & n_tricycle(x2) & n_person(x1))
exists e1 x1 x2 x3.(n_tricycle(x3) & n_person(x1) & on(e1,x3) & Theme(e1,x2) & Actor(e1,x1) & v_do(e1) & n_trick(x2))