A man and a woman are walking across a street.
a couple are walking
Not all man and a woman walking across a street are a couple.
exists e1 x1 x2 x3 x4.(across(e1,x4) & n_street(x4) & Actor(e1,x1) & v_walk(e1) & subset_of(x3,x1) & n_woman(x3) & subset_of(x2,x1) & n_man(x2))
exists e1 x1.(Actor(e1,x1) & v_walk(e1) & n_couple(x1))