def METHOD_NAME(k, r0, td, tb, tau):
    """Term in Eq. 39 in Zhang+95."""
    if k == 0:
        return A0(r0, td, tb, tau)
    # Equation 39
    s = 0
    for n in range(1, INFINITE):
        s += h(k + 1, n, td, tb, tau) - 2 * h(k, n, td, tb, tau) + h(k - 1, n, td, tb, tau)
    return r0 * tb * s