Relation between [C/Fe] and [Na/Fe] computed, A) with the model parameters T_efflog g and v_t given in Monaco et al. (2012), and B) with the same parameters but v_t =1.3 km s^-1. The red squares represent the subgiant stars which have a temperature below 5600 K. The blue dots are for the turnoff stars with 5600 K < T_eff < 5980 K. The very Li-rich star M4-37934 is surrounded by a red circle. A typical value of the total error is represented by the cross at the lower left corner of the figure. The mean values obtained for the two groups of RGB stars in M 4 by Villanova & Geisler (2011): C-rich N-poor stars and the C-poor N-rich stars are shown by black open stars symbols.