The young man is surfing.
A boy is playing in a sandbox.
One can not be surfing and in a sandbox simultaneously.
exists e1 s1 x1.(n_man(x1) & a_young(s1) & Theme(s1,x1) & Actor(e1,x1) & v_surf(e1))
exists e1 x1 x2.(in(e1,x2) & n_sandbox(x2) & Actor(e1,x1) & v_play(e1) & n_boy(x1))