Boy does skateboard trick.
A child is skateboarding.
If the boy does a trick on a skateboard, he must be skateboarding.
exists e1 x1 x2.(ne_nam_boy(x1) & Theme(e1,x2) & Actor(e1,x1) & v_skateboard(e1) & n_trick(x2))
exists e1 x1.(Actor(e1,x1) & v_skateboard(e1) & n_child(x1))