def arc(start_x, start_y, end_x, end_y, start_degrees, end_degrees)
      primitive 'arc ' + format('%g,%g %g,%g %g,%g',
                                start_x, start_y, end_x, end_y, start_degrees, end_degrees)
    end
def arc(start_x, start_y, end_x, end_y, start_degrees, end_degrees)
      primitive 'arc ' + format('%g,%g %g,%g %g,%g',
                                start_x, start_y, end_x, end_y, start_degrees, end_degrees)
    end
Draw an arc.