A man is playing the flute and there is another instrumentalist behind him.
The man is in a band.
Just because a man is playing a musical instrument with another person doesn't mean he's part of a band.
exists e1 p1 x1 x2 x3 x4.(n_male(x2) & n_instrumentalist(x4) & n_flute(x2) & exists x5.((x3 = x5) & behind(x5,x2) & n_instrumentalist(x5) & -(x5 = x4)) & Theme(e1,x2) & Actor(e1,x1) & v_play(e1) & n_man(x1))
exists p1 x1.(n_man(x1) & exists x2.(in(x1,x2) & n_band(x2)))