def prox_line(xy, step):
    """2D projection onto 2 lines"""
    return np.concatenate((prox_xline(xy[0], step), prox_yline(xy[1], step)))
def prox_line ( xy , step ) : return np . concatenate ( ( prox_xline ( xy [ 0 ] , step ) , prox_yline ( xy [ 1 ] , step ) ) )
2D projection onto 2 lines