Two people ride the train.
A couple rides a train.
Not all people are a couple.
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.(Theme(e1,x2) & Actor(e1,x1) & v_ride(e1) & n_train(x2) & n_couple(x1))