three boys and a mom at the harbor.
Four people are watching some boats.
There is no way of knowing what the people are doing at the harbor; they could be watching some boats, they could be turned away from the boats, they could be in a store at the harbor or there may be no boats in sight.  There are many other options for the people's current activities.
exists s1 x1 x2 x3.(n_harbor(x3) & a_topic(s1) & subset_of(x2,s1) & at(x2,x3) & n_mom(x2) & subset_of(x1,s1) & n_boy(x1) & card_eq_3(x1))
exists e1 x1 x2.(Theme(e1,x2) & Actor(e1,x1) & v_watch(e1) & n_boat(x2) & n_people(x1) & card_eq_4(x1))