[C/Fe] as a function of luminosity for our sample (squares), split in stars that have spatial and kinematic properties compatible with membership to the Sag stream (green) and not compatible (purple), as described in Sect. 7 (see also Fig. 14). The dashed line indicates the Aoki et al. (2007) criterion for identifying carbon-enhanced metal-poor stars when taking into account evolutionary effects after the first dredge up; the solid line shows the trend of declining [C/Fe] with increasing stellar luminosity in three MW globular clusters as in (see Kirby et al. 2015), which also agrees with the trends observed in that same work for the MW classical dSphs Ursa Minor, Draco, Sculptor and Fornax. In the corner we give a representative error-bar.