A group of guys are standing on a stage playing several different instruments.
A group of guys are performing a rock song.
A group of guys standing on a stage playing several different instruments doesn't mean that they are performing a rock song.
exists e2 e1 s1 x1 x2 x3 x4 x5.(n_instrument(x5) & for(e1,e2) & Theme(e2,x4) & Actor(e2,x1) & v_play(e2) & -(x4 = x5) & n_instrument(x4) & a_several(s1) & Theme(s1,x4) & on(e1,x3) & n_stage(x3) & Actor(e1,x1) & v_stand(e1) & of(x1,x2) & n_guy(x2) & n_group(x1))
exists e1 x1 x2 x3 x4.(Theme(e1,x3) & Actor(e1,x1) & v_perform(e1) & n_song(x3) & of(x3,x4) & n_rock(x4) & of(x1,x2) & n_guy(x2) & n_group(x1))