Workers are cleaning railroad tracks.
Workers are on railroad tracks.
In order to be cleaning railroad tracks workers would have to be on the railroad tracks.
exists e1 x1 x2 x3.(Theme(e1,x2) & Actor(e1,x1) & v_clean(e1) & n_track(x2) & of(x2,x3) & n_railroad(x3) & n_worker(x1))
exists p1 x1.(exists x2 x3.(on(x1,x2) & n_track(x2) & of(x2,x3) & n_railroad(x3)) & n_worker(x1))