Left: [¹²C/¹³C] ratio as a function of the mixing factor f_mix, which represents the fraction of material processed by helium burning mixed with the material processed by hydrogen burning. Two compositions are tested for the material processed by hydrogen burning: a C-rich composition (red line) and a C-poor composition (black line). Right: green histogram showing the distribution of the CEMP-no stars used in this work. They belong to class 2 or 4. The grey histogram shows all known CEMP-no stars with a measured ¹²C/¹³C ratio.