def _hab_s(s):
    """Define the boundary between Region 2a and 2b, h=f(s)

    Parameters
    ----------
    s : float
        Specific entropy, [kJ/kgK]

    Returns
    -------
    h : float
        Specific enthalpy, [kJ/kg]

    References
    ----------
    IAPWS, Revised Supplementary Release on Backward Equations for Pressure
    as a Function of Enthalpy and Entropy p(h,s) for Regions 1 and 2 of the
    IAPWS Industrial Formulation 1997 for the Thermodynamic Properties of
    Water and Steam, http://www.iapws.org/relguide/Supp-PHS12-2014.pdf, Eq 2

    Examples
    --------
    >>> _hab_s(7)
    3376.437884
    """
    smin = _Region2(_TSat_P(4), 4)["s"]
    smax = _Region2(1073.15, 4)["s"]
    if s < smin:
        h = 0
    elif s > smax:
        h = 5000
    else:
        h = -0.349898083432139e4 + 0.257560716905876e4*s - \
            0.421073558227969e3*s**2+0.276349063799944e2*s**3
    return h
Define the boundary between Region 2a and 2b, h=f(s)

    Parameters
    ----------
    s : float
        Specific entropy, [kJ/kgK]

    Returns
    -------
    h : float
        Specific enthalpy, [kJ/kg]

    References
    ----------
    IAPWS, Revised Supplementary Release on Backward Equations for Pressure
    as a Function of Enthalpy and Entropy p(h,s) for Regions 1 and 2 of the
    IAPWS Industrial Formulation 1997 for the Thermodynamic Properties of
    Water and Steam, http://www.iapws.org/relguide/Supp-PHS12-2014.pdf, Eq 2

    Examples
    --------
    >>> _hab_s(7)
    3376.437884