The sailboarder is falling in the water.
The sailboarder is falling in the lava.
A water is not same as a lava.
exists e1 x1 x2.(n_water(x2) & n_sailboarder(x1) & in(e1,x2) & Actor(e1,x1) & v_fall(e1))
exists e1 x1 x2.(n_lava(x2) & n_sailboarder(x1) & in(e1,x2) & Actor(e1,x1) & v_fall(e1))