a skateboarder grinds a rail.
A skateboarder doing a flip off a ramp.
One either grinds or does a flip.
exists e1 x1 x2.(Theme(e1,x2) & Actor(e1,x1) & v_grind(e1) & n_rail(x2) & n_skateboarder(x1))
exists e1 x1 x2 x3 x4.(a_topic(x1) & Theme(e1,x3) & Actor(e1,x2) & v_do(e1) & off(x3,x4) & n_ramp(x4) & n_flip(x3) & (x1 = x2) & n_skateboarder(x1))