People playing in the water with a water bike.
There is no one in the water.
People can't be playing in the water if there is no one in the water.
exists e1 x1 x2 x3 x4.(a_topic(x1) & with(e1,x4) & n_bike(x4) & of(x4,x3) & n_water(x3) & n_water(x3) & in(e1,x3) & Actor(e1,x2) & v_play(e1) & (x1 = x2) & n_people(x1))
exists p1 x1 x3.(n_water(x3) & -exists x2.((x1 = x2) & in(x2,x3) & n_one(x2)))