Two people are sleeping on a sofa.
Nobody is sleeping
Two people cannot be sleeping if nobody is sleeping.
exists e1 x1 x2.(on(e1,x2) & n_sofa(x2) & Actor(e1,x1) & v_sleep(e1) & n_people(x1) & card_eq_2(x1))
-exists e1 x1.(Actor(e1,x1) & v_sleep(e1) & n_person(x1))