People are walking up and down the streets.
People walk on the streets.
For people to be walking the streets people must be on the streets. Therefore people are walking on the streets.
exists e1 e2 s1 x1 x2 x3.(n_street(x3) & down(e2,x3) & Actor(e2,x2) & v_walk(e2) & n_people(x2) & a_up(s1) & Manner(e1,s1) & Actor(e1,x1) & v_walk(e1) & n_people(x1))
exists e1 x1 x2.(n_street(x2) & on(e1,x2) & Actor(e1,x1) & v_walk(e1) & n_people(x1))