A street artist is at work.
An artist is working on a piece of art.
An artist working on art refines artist at work.
exists p1 x1 x2.(exists x3.(at(x1,x3) & n_work(x3)) & n_artist(x1) & of(x1,x2) & n_street(x2))
exists e1 x1 x2 x3.(on(e1,x2) & of(x2,x3) & n_art(x3) & n_piece(x2) & Actor(e1,x1) & v_work(e1) & n_artist(x1))