Comparison of the abundance ratios [O/N] and [C/N] of CEMP-no stars with model data. The same codes as in Fig. 1 are adopted to represent the observations and models. The small red rectangles show the AGB models by Herwig (2004) connected by a red broken line. The general trend of the CNO burning is represented by a big reddish arrow. The small vertical arrows indicate upper limits for [O/Fe] and the small oblique arrows upper limits for [N/Fe]. The star HE 1201-1512 was not indicated because of many lower limits.