Observations of ¹²C/¹³C in planetary nebulae as a function of the progenitor mass (Palla et al. 2000). Squares and triangles are respectively for actual determinations and lower limits of the carbon isotopic ratio. Black and blue theoretical lines have the same meaning as in Fig. 17, while red curves show the model predictions at the AGB tip for the low-mass models that were computed up to that phase (solid and dashed red curves are respectively for the models with thermohaline mixing only and for the models with thermohaline and rotation-induced mixing).