The boys play on the rocks overlooking the valley.
The boys are brothers.
Not all boys are brothers
exists e2 e1 x1 x2 x3.(n_valley(x3) & n_rock(x2) & n_boy(x1) & for(e1,e2) & Theme(e2,x3) & Actor(e2,x1) & v_overlook(e2) & on(e1,x2) & Actor(e1,x1) & v_play(e1))
exists p1 x1.(n_boy(x1) & exists x2.((x1 = x2) & n_brother(x2)))