Top two panels: Surface luminosity (top) and helium luminosity (bottom) during the ninth thermal pulse of the sequence with M_in = 1.5 M_⊙. Four stages, labeled as a, b, c, and d, are highlighted, which correspond to the chemical stratifications shown in the four bottom panels. Bottom panels: Formation of the O peak during the thermal pulses. Panels b and c show that the O peak is formed in the same way using both prescriptions, while panel d shows how the additional instabilities considered in MLT♯ lead to the mixing of the O peak formed in the previous TP. We also highlight the position of the eighth and ninth O peaks.