[F/Ba] vs. [Ba/Fe] in the sample stars with [Fe/H] ~ −1.0 (top) and ~ −2.0 (bottom). Symbols as Fig. 1; colour code: black, normal galactic C-stars; blue, extragalactic C-stars; magenta, CH/Ba stars (see text). Continuous lines are theoretical predictions for a non-rotating 1.5 M_⊙ TP-AGB star with metallicity Z ~ 10⁻³ and 10⁻⁴ in the top and bottom panels, as labelled respectively, according to Cristallo et al. (2015). We note that for these low metallicities, theoretically AGB stars become carbon rich from the very first TPs.