People walk down the busy sidewalk.
People are walking.
Walking is a rephrase of walk down.
exists e1 s1 x1 x2.(n_sidewalk(x2) & a_busy(s1) & Theme(s1,x2) & down(e1,x2) & Actor(e1,x1) & v_walk(e1) & n_people(x1))
exists e1 x1.(Actor(e1,x1) & v_walk(e1) & n_people(x1))