Two men playing guitars are singing at a concert.
The two men playing at the concert are on tour.
Just because they are singing at the concert, it does not mean they are on tour.
exists e1 e2 x1 x2 x3 x4.(at(e2,x4) & n_concert(x4) & Actor(e2,x1) & v_sing(e2) & Theme(e1,x3) & Actor(e1,x2) & v_play(e1) & n_guitar(x3) & (x1 = x2) & n_man(x1) & card_eq_2(x1))
exists e1 p1 x1 x2 x3.(n_concert(x3) & n_man(x1) & card_eq_2(x1) & exists x4.(on(x1,x4) & n_tour(x4)) & at(e1,x3) & Actor(e1,x2) & v_play(e1) & (x1 = x2))