A man playing a guitar on stage under red light.
The man is a musician.
Not all men playing a guitar is a musician. He could just be part of the road crew testing the guitar.
exists e1 s1 x1 x2 x3 x4 x5.(a_topic(x1) & under(e1,x5) & n_light(x5) & a_red(s1) & Theme(s1,x5) & on(e1,x4) & n_stage(x4) & Theme(e1,x3) & Actor(e1,x2) & v_play(e1) & n_guitar(x3) & (x1 = x2) & n_man(x1))
exists p1 x1.(n_man(x1) & exists x2.((x1 = x2) & n_musician(x2)))