A person does a trick on a bike.
The person is doing tricks on their bikes.
A person references a single one, and bikes references numerous.
exists e1 x1 x2 x3.(on(e1,x3) & n_bike(x3) & Theme(e1,x2) & Actor(e1,x1) & v_do(e1) & n_trick(x2) & n_person(x1))
exists e1 x1 x2 x3.(n_bike(x3) & of(x3,x1) & n_thing(x1) & n_person(x1) & on(e1,x3) & Theme(e1,x2) & Actor(e1,x1) & v_do(e1) & n_trick(x2))