A boy skateboards down the metal handrail at night.
The boy is grinding down a staircase.
If he's grinding down the staircase, he's not on the handrail.
exists e1 x1 x2 x3 x4.(n_handrail(x2) & of(x2,x3) & n_metal(x3) & at(e1,x4) & n_night(x4) & down(e1,x2) & Actor(e1,x1) & v_skateboard(e1) & n_boy(x1))
exists e1 s1 x1 x2.(n_boy(x1) & a_down(s1) & Manner(e1,s1) & Theme(e1,x2) & Actor(e1,x1) & v_grind(e1) & n_staircase(x2))