Two guys rocking out on guitars.
Two guys play the cello while singing.
they were singing for the guitar's tone
exists e1 s1 x1 x2 x3.(a_topic(x1) & a_out(s1) & Manner(e1,s1) & on(e1,x3) & n_guitar(x3) & Actor(e1,x2) & v_rock(e1) & (x1 = x2) & n_guy(x1) & card_eq_2(x1))
exists e1 e2 x1 x2.(n_cello(x2) & while(e1,e2) & Actor(e2,x1) & v_sing(e2) & Theme(e1,x2) & Actor(e1,x1) & v_play(e1) & n_guy(x1) & card_eq_2(x1))