The snowboarder is sitting down.
the snowboarder goes down the hill
The snowboarder cannot be sitting down as well as going down the hill at the same time.
exists e1 s1 x1.(n_snowboarder(x1) & a_down(s1) & Manner(e1,s1) & Actor(e1,x1) & v_sit(e1))
exists e1 x1 x2.(n_hill(x2) & n_snowboarder(x1) & down(e1,x2) & Actor(e1,x1) & v_go(e1))