A group of girls are riding on a roller coaster.
No one is on the roller coaster.
When a group of girls are riding there cant be no one on roller coaster.
exists e1 x1 x2 x3 x4.(on(e1,x3) & n_coaster(x3) & of(x3,x4) & n_roller(x4) & Actor(e1,x1) & v_ride(e1) & of(x1,x2) & n_girl(x2) & n_group(x1))
exists x2 x3.(n_coaster(x2) & of(x2,x3) & n_roller(x3) & -exists p1 x1.(on(x1,x2) & n_one(x1)))