People are walking down a street.
People are on a roller coaster.
The People are either  walking down a street or on a roller coaster.
exists e1 x1 x2.(down(e1,x2) & n_street(x2) & Actor(e1,x1) & v_walk(e1) & n_people(x1))
exists p1 x1.(exists x2 x3.(on(x1,x2) & n_coaster(x2) & of(x2,x3) & n_roller(x3)) & n_people(x1))