The man is on a ski boat in the water.
There's a man on a ski boat in the lake.
The man is on a ski boat in the water but not in the lake.
exists p1 x1 x4.(n_water(x4) & n_man(x1) & exists x2 x3.(on(x1,x2) & in(x2,x4) & n_boat(x2) & of(x2,x3) & n_ski(x3)))
exists p1 x1 x2.(n_lake(x2) & in(p1,x2) & exists x3 x4 x5.((x1 = x3) & on(x3,x4) & n_boat(x4) & of(x4,x5) & n_ski(x5) & n_man(x3)))