Four people standing on a boat on the lake.
Four people are sailing.
The people in the boat may not be sailing.  They may be paddling or the boat may have a motor.
exists e1 x1 x2 x3 x4.(n_lake(x4) & a_topic(x1) & on(e1,x4) & on(e1,x3) & n_boat(x3) & Actor(e1,x2) & v_stand(e1) & (x1 = x2) & n_people(x1) & card_eq_4(x1))
exists p1 x1.(exists x2.((x1 = x2) & n_sailing(x2)) & n_people(x1) & card_eq_4(x1))