A man is working on an art piece.
The man is a painter.
Just because a man is working on art is does not mean that he is a painter.
exists e1 x1 x2 x3.(on(e1,x2) & n_piece(x2) & of(x2,x3) & n_art(x3) & Actor(e1,x1) & v_work(e1) & n_man(x1))
exists p1 x1.(n_man(x1) & exists x2.((x1 = x2) & n_painter(x2)))