A skateboarder is balancing on the rail of stairs.
A skateboarder is balancing on a rail.
rail is a form of stairs.
exists e1 x1 x2 x3.(n_rail(x2) & on(e1,x2) & of(x2,x3) & n_stair(x3) & Actor(e1,x1) & v_balance(e1) & n_skateboarder(x1))
exists e1 x1 x2.(on(e1,x2) & n_rail(x2) & Actor(e1,x1) & v_balance(e1) & n_skateboarder(x1))