Two men are on a police boat.
The men are fishing on a police boat.
The men are on a police boat but that doesn't necessarily imply that they are fishing.
exists p1 x1.(exists x2 x3.(on(x1,x2) & n_boat(x2) & of(x2,x3) & n_police(x3)) & n_man(x1) & card_eq_2(x1))
exists e1 x1 x2 x3.(n_man(x1) & on(e1,x2) & n_boat(x2) & of(x2,x3) & n_police(x3) & Actor(e1,x1) & v_fish(e1))