People are at a party at night.
The people are at a house party.
Not every party at night is a house party.
exists p1 x1 x2.(at(p1,x2) & n_night(x2) & exists x3.(at(x1,x3) & n_party(x3)) & n_people(x1))
exists p1 x1.(n_people(x1) & exists x2 x3.(at(x1,x2) & n_party(x2) & of(x2,x3) & n_house(x3)))