a skateboarder grinds a curb.
A skater skates on a sidewalk.
The skateboarder is grinding a curb on the sidewalk.
exists e1 x1 x2.(Theme(e1,x2) & Actor(e1,x1) & v_grind(e1) & n_curb(x2) & n_skateboarder(x1))
exists e1 x1 x2.(on(e1,x2) & n_sidewalk(x2) & Actor(e1,x1) & v_skate(e1) & n_skater(x1))