[F/Fe] vs. [Fe/H] in the stars analysed here (filled circles) and in previous studies (open circles, see text). Colour code: black, normal (N-type) Galactic carbon stars; green, SC-type stars; blue, extragalactic carbon stars; magenta, extrinsic Ba/CH stars. Dashed lines represent theoretical predictions for a non-rotating 2 M_⊙ (for [Fe/H] > −0.5) and 1.5 M_⊙ (for [Fe/H] < −0.5) AGB star at different TPs, according to Cristallo et al. (2015). A typical error bar is indicated.