A boy sitting down at the park.
The boy is standing on the grass.
A person cannot be sitting down and standing at the same time.
exists e1 s1 x1 x2 x3.(n_park(x3) & a_topic(x1) & at(e1,x3) & a_down(s1) & Manner(e1,s1) & Actor(e1,x2) & v_sit(e1) & (x1 = x2) & n_boy(x1))
exists e1 x1 x2.(n_grass(x2) & n_boy(x1) & on(e1,x2) & Actor(e1,x1) & v_stand(e1))