A group of workers at a train station.
No one is at the train station.
It is either a group of workers or no one.
exists x1 x2 x3 x4.(a_topic(x1) & at(x1,x3) & n_station(x3) & of(x3,x4) & n_train(x4) & of(x1,x2) & n_worker(x2) & n_group(x1))
exists x2 x3.(n_station(x2) & of(x2,x3) & n_train(x3) & -exists p1 x1.(at(x1,x2) & n_one(x1)))