A snowboarder is doing a trick.
The snowboarder did a flip.
A snowboarder is doing a trick does not necessary that he did a flip.
exists e1 x1 x2.(Theme(e1,x2) & Actor(e1,x1) & v_do(e1) & n_trick(x2) & n_snowboarder(x1))
exists e1 x1 x2.(n_snowboarder(x1) & Theme(e1,x2) & Actor(e1,x1) & v_do(e1) & n_flip(x2))