People are outside at night.
Nobody is outside.
People and nobody are not same.
exists s1 x1 x2.(at(s1,x2) & n_night(x2) & Theme(s1,x1) & a_outside(s1) & n_people(x1))
-exists s1 x1.(Theme(s1,x1) & a_outside(s1) & n_person(x1))