The young boys are looking for apples that do n't exist.
The young boys are looking for unicorns that don't exist.
Unicorns are not apples.
exists e1 s1 x1 x2 x3.(n_boy(x1) & a_young(s1) & Theme(s1,x1) & for(e1,x2) & -exists e2.(Actor(e2,x3) & v_exist(e2)) & (x2 = x3) & n_apple(x2) & Actor(e1,x1) & v_look(e1))
exists e1 s1 x1 x2 x3.(n_boy(x1) & a_young(s1) & Theme(s1,x1) & for(e1,x2) & -exists e2.(Actor(e2,x3) & v_exist(e2)) & (x2 = x3) & n_unicorn(x2) & Actor(e1,x1) & v_look(e1))