Carbon and oxygen abundances of AGB and post-AGB objects in the Galactic disk as compared with the predictions of the Z₀ = 0.02 (upper set) and Z₀ = 0.01 sequences (lower set). Tracks in blue lines correspond to those that experience significant 3DUP, while thick black lines indicate sequences with no significant 3DUP. The red line corresponds to the evolution of the 4 M_⊙ (Z₀ = 0.02) sequence that experiences both 3DUP and hot-bottom burning. Abundances are presented in the customary astronomical scale for logarithmic abundances, log ϵ_X = log  (N_X/N_H) + 12, where N_X and N_H are the number densities of elements X and H, respectively.