code: def Ttr(x):
      
      if 0 <= x <= 0.33367:
          Ttr = 273.16*(1-0.3439823*x-1.3274271*x**2-274.973*x**3)
      elif 0.33367 < x <= 0.58396:
          Ttr = 193.549*(1-4.987368*(x-0.5)**2)
      elif 0.58396 < x <= 0.81473:
          Ttr = 194.38*(1-4.886151*(x-2/3)**2+10.37298*(x-2/3)**3)
      elif 0.81473 < x <= 1:
          Ttr = 195.495*(1-0.323998*(1-x)-15.87560*(1-x)**4)
      else:
          raise NotImplementedError("Incoming out of bound")
      return Ttr
docs: Equation for the triple point of ammonia-water mixture
  
      Parameters
      ----------
      x : float
          Mole fraction of ammonia in mixture, [mol/mol]
  
      Returns
      -------
      Ttr : float
          Triple point temperature, [K]
  
      Notes
      ------
      Raise :class:`NotImplementedError` if input isn't in limit:
  
          * 0 ≤ x ≤ 1
  
      References
      ----------
      IAPWS, Guideline on the IAPWS Formulation 2001 for the Thermodynamic
      Properties of Ammonia-Water Mixtures,
      http://www.iapws.org/relguide/nh3h2o.pdf, Eq 9