Evolution of the surface lithium abundance, of the carbon isotopic ratio ¹²C/¹³C, of [C/Fe], and [N/Fe] as a function of the luminosity logarithm for three simulations where the diffusion coefficient has been changed. The full line (labeled “BGS”) was obtained implementing the Brown et al. (2013) prescription, the dashed line (labeled “BGS x 10”) corresponds to the case where the diffusion coefficient is artificially increased by a factor of 10, and the dotted line (labeled “BGS x 100”) refers to computation with a diffusion coefficient 100 times larger than that of Brown et al. (2013). The luminosity of the model at the moment of the first dredge-up and at the start of the luminosity bump are marked in the top panel.