code: def _hab_s(s):
      
      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
docs: 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