People are standing on a train platform waiting for the train.
A group of people are roller skating.
People waiting for the train can not be roller skating at the same time.
exists e1 e2 x1 x2 x3.(for(e1,e2) & for(e2,x3) & n_train(x3) & n_train(x3) & Actor(e2,x1) & v_wait(e2) & on(e1,x2) & n_platform(x2) & of(x2,x3) & Actor(e1,x1) & v_stand(e1) & n_people(x1))
exists e1 x1 x2 x3.(Time(e1,x3) & n_roller(x3) & Actor(e1,x1) & v_skate(e1) & of(x1,x2) & n_people(x2) & n_group(x1))