A little girl is sitting on a toy tractor.
A boy sitting on a tractor
There can either be a boy or a girl.
exists e1 s1 x1 x2 x3.(on(e1,x2) & n_tractor(x2) & of(x2,x3) & n_toy(x3) & Actor(e1,x1) & v_sit(e1) & n_girl(x1) & a_little(s1) & Theme(s1,x1))
exists e1 x1 x2 x3.(a_topic(x1) & on(e1,x3) & n_tractor(x3) & Actor(e1,x2) & v_sit(e1) & (x1 = x2) & n_boy(x1))