A group of people playing polo.
A family is playing polo.
Not all groups of people are a family.
exists e1 x1 x2 x3 x4.(a_topic(x1) & of(x1,x2) & Theme(e1,x4) & Actor(e1,x3) & v_play(e1) & n_polo(x4) & (x2 = x3) & n_people(x2) & n_group(x1))
exists e1 x1 x2.(Theme(e1,x2) & Actor(e1,x1) & v_play(e1) & n_polo(x2) & n_family(x1))