Evolution up to the AGB tip of C, N, and O elemental and isotopic ratios in models with 1.5 M_⊙ (black line) and 2 M_⊙ (red line). The first dredge up occurs at log t/ (t−t_f) ~ 0.9 (1.5 M_⊙) and 0.6 (2 M_⊙), while the RGB bump takes place at log t/ (t−t_f) ~ 1.2 and 0.8, respectively. The combined actions of the third dredge up and the AGB extra mixing arise at log t/ (t−t_f) > 3.2 and 2.8. Note the reduced scale in the ¹⁴N/¹⁵N ratio.