The girl is on the treadmill.
The girl is on an exercise machine.
a treadmill is an exercise machine
exists p1 x1 x2.(n_treadmill(x2) & n_girl(x1) & on(x1,x2))
exists p1 x1.(n_girl(x1) & exists x2 x3.(on(x1,x2) & n_machine(x2) & of(x2,x3) & n_exercise(x3)))