People walk across a crosswalk.
people cross a sidewalk
A sidewalk is something people cross.
exists e1 x1 x2.(across(e1,x2) & n_crosswalk(x2) & Actor(e1,x1) & v_walk(e1) & n_people(x1))
exists e1 x1 x2.(Theme(e1,x2) & Actor(e1,x1) & v_cross(e1) & n_sidewalk(x2) & n_people(x1))