Two people ride the train.
People having a conversation on the train.
Not all people are having a conversation.
exists e1 x1 x2.(n_train(x2) & Theme(e1,x2) & Actor(e1,x1) & v_ride(e1) & n_people(x1) & card_eq_2(x1))
exists e1 x1 x2 x3 x4.(n_train(x4) & a_topic(x1) & Theme(e1,x3) & Actor(e1,x2) & v_have(e1) & on(x3,x4) & n_conversation(x3) & (x1 = x2) & n_people(x1))