Protesters walking down the street holding Palestinian flags.
Protesters are walking on the street holding flags.
Walking down the street implies the action of walking physically on the street, which is rephrased as walking on the street.
exists e2 e1 s1 x1 x2 x3 x4.(n_street(x3) & a_topic(x1) & for(e1,e2) & Theme(e2,x4) & Actor(e2,x2) & v_hold(e2) & n_flag(x4) & a_palestinian(s1) & Theme(s1,x4) & down(e1,x3) & Actor(e1,x2) & v_walk(e1) & (x1 = x2) & n_protester(x1))
exists e1 e2 x1 x2 x3.(n_street(x2) & for(e1,e2) & Theme(e2,x3) & Actor(e2,x1) & v_hold(e2) & n_flag(x3) & on(e1,x2) & Actor(e1,x1) & v_walk(e1) & n_protester(x1))