[O/Fe] vs. [Na/Fe]. Red symbols correspond to this study where the open red symbol corresponds to the peculiar Star #7. Black symbols correspond to GGC data from Carretta et al. (2009a), and gray symbols to halo and disk field stars from Fulbright (2000), Reddy et al. (2003), and Reddy et al. (2006). Blue solid lines correspond to the dilution model from Carretta et al. (2009b) for NGC 7078 (M15) and NGC 2808. The red dash-dotted line is the dilution model for NGC 4372 considering the full sample of stars and the red dashed line is the dilution model but excluding Star #7. The black lines are the empirical separations into primordial, intermediate, and extreme populations according to Carretta et al. (2009b). The star-to-star error bar is indicated.