Two children are laughing in the grass.
the children are siblings
Two children laughing in the grass are not necessarily siblings.
exists e1 x1 x2.(n_grass(x2) & in(e1,x2) & Actor(e1,x1) & v_laugh(e1) & n_child(x1) & card_eq_2(x1))
exists p1 x1.(n_child(x1) & exists x2.((x1 = x2) & n_sibling(x2)))