A boy on a skateboard balances on a red beam.
The boy is on a bike.
One cannot be on a skateboard and a bike simultaneously.
exists e1 s1 x1 x2 x3.(on(e1,x3) & n_beam(x3) & a_red(s1) & Theme(s1,x3) & Actor(e1,x1) & v_balance(e1) & on(x1,x2) & n_skateboard(x2) & n_boy(x1))
exists p1 x1.(n_boy(x1) & exists x2.(on(x1,x2) & n_bike(x2)))