[Mg/Fe] vs. [M/H] abundance diagram for the delayed two-infall model scenario of chemical evolution with François et al. (2004) yields (upper panel) and Kobayashi et al. (2006) yields (lower panel). The colour bar indicates the predicted stellar number counts (normalised to the maximum value) at a certain point of the diagram, taking into account the selection function. The light blue points are the observed high-α stars, whereas the orange points are the observed low-α stars. The magenta contour lines enclose the observed density distribution of stars.