docs: def plot4_nolog(self, num):
          """
             Plots the abundances of H-1, He-4, C-12 and O-16.
          """
          self.plot_prof_2(num,'H-1',0.,5.)
          self.plot_prof_2(num,'He-4',0.,5.)
          self.plot_prof_2(num,'C-12',0.,5.)
          self.plot_prof_2(num,'O-16',0.,5.)
          pyl.legend(loc=3)