Solid curves: abundance patterns predicted at the surface of unevolved low-mass stars, obtained by mixing 1% of the matter ejected by AGB models with 0.2  M_⊙ of their envelopes. The AGB models are identified by their initial mass and metallicity, as reported in the bottom right and top left corner of each panel. The circles show the abundances measured in extremely metal-poor stars selected from the SAGA database (see the top right label in each plot).