A person on a bmx bike.
The BMX bike is black.
The BMX bike could be another color besides black.
exists x1 x2 x3.(a_topic(x1) & on(x1,x2) & n_bike(x2) & of(x2,x3) & n_bmx(x3) & n_person(x1))
exists s1 x1 x2.(n_bike(x1) & (x1 = x2) & ne_org_bmx(x2) & Theme(s1,x1) & a_black(s1))