Similar to :func:`_pull_out_perm_lhs` but on the RHS of a series
    product self-feedback.

def _pull_out_perm_rhs(rest, rhs, out_port, in_port):
    """Similar to :func:`_pull_out_perm_lhs` but on the RHS of a series
    product self-feedback."""
    in_im, rhs_red = rhs._factor_rhs(in_port)
    return (Feedback.create(
                SeriesProduct.create(*rest),
                out_port=out_port, in_port=in_im) << rhs_red)