People walking in front of a billboard.
People are walking a dog in front of a billboard.
Walking does not imply walking a dog.
exists e1 x1 x2 x3 x4.(a_topic(x1) & in(e1,x3) & of(x3,x4) & n_billboard(x4) & n_front(x3) & Actor(e1,x2) & v_walk(e1) & (x1 = x2) & n_people(x1))
exists e1 x1 x2 x3 x4.(in(e1,x3) & of(x3,x4) & n_billboard(x4) & n_front(x3) & Theme(e1,x2) & Actor(e1,x1) & v_walk(e1) & n_dog(x2) & n_people(x1))