The man is playing a guitar.
A man is writing a guitar song for his friend.
Playing guitar does not mean writing a song for his friend.
exists e1 x1 x2.(n_man(x1) & Theme(e1,x2) & Actor(e1,x1) & v_play(e1) & n_guitar(x2))
exists e1 x1 x2 x3 x4.(Theme(e1,x2) & Actor(e1,x1) & v_write(e1) & for(x2,x4) & n_friend(x4) & of(x4,x1) & n_male(x1) & n_song(x2) & of(x2,x3) & n_guitar(x3) & n_man(x1))