A man and a woman are standing on the curb.
A man and woman are waiting for a taxi.
People can stand on a curb without necessarily waiting for a taxi.
exists e1 x1 x2 x3 x4.(n_curb(x4) & on(e1,x4) & Actor(e1,x1) & v_stand(e1) & subset_of(x3,x1) & n_woman(x3) & subset_of(x2,x1) & n_man(x2))
exists e1 x1 x2 x3 x4.(for(e1,x4) & n_taxi(x4) & Actor(e1,x1) & v_wait(e1) & n_woman(x3) & n_man(x2) & subset_of(x3,x1) & subset_of(x2,x1))