The boy is skateboarding on the bench by the fence.
A boy wearing a helmet is on a skateboard.
Not everyone who goes skateboarding wears a helmet.
exists e1 x1 x2 x3.(n_fence(x3) & n_bench(x2) & n_boy(x1) & by(e1,x3) & on(e1,x2) & Actor(e1,x1) & v_skateboard(e1))
exists e1 p1 x1 x2 x3.(exists x4.(on(x1,x4) & n_skateboard(x4)) & Theme(e1,x3) & Actor(e1,x2) & v_wear(e1) & n_helmet(x3) & (x1 = x2) & n_boy(x1))