People crossing a city street.
People cross the street.
People crossing the street is used as happening now, while people cross the street is a general statement.
exists e1 x1 x2 x3 x4.(a_topic(x1) & Theme(e1,x3) & Actor(e1,x2) & v_cross(e1) & n_street(x3) & of(x3,x4) & n_city(x4) & (x1 = x2) & n_people(x1))
exists e1 x1 x2.(n_street(x2) & Theme(e1,x2) & Actor(e1,x1) & v_cross(e1) & n_people(x1))