A man watches two small boys playing in a naturally formed rock.
Nobody is watching.
A man is watching or nobody is watching.
exists e1 e2 e3 s1 x1 x2 x3 x4.(Theme(e3,x2) & Actor(e3,x1) & v_watch(e3) & in(e1,x4) & n_rock(x4) & Theme(e2,x4) & v_form(e2) & r_naturally(x4) & Actor(e1,x3) & v_play(e1) & (x2 = x3) & n_boy(x2) & a_small(s1) & Theme(s1,x2) & card_eq_2(x2) & n_man(x1))
-exists e1 x1.(Actor(e1,x1) & v_watch(e1) & n_person(x1))