A boy and a girl are standing on a riverbank facing the water.
The boy and girl are siblings.
Just because a boy and girl are standing on a riverbank facing the river, it does not mean that the boy and girl are siblings.
exists e2 e1 x1 x2 x3 x4 x5.(n_water(x5) & for(e1,e2) & Theme(e2,x5) & Actor(e2,x1) & v_face(e2) & on(e1,x4) & n_riverbank(x4) & Actor(e1,x1) & v_stand(e1) & subset_of(x3,x1) & n_girl(x3) & subset_of(x2,x1) & n_boy(x2))
exists p1 x1 x2 x3.(n_girl(x3) & n_boy(x2) & subset_of(x3,x1) & subset_of(x2,x1) & exists x4.((x1 = x4) & n_sibling(x4)))