As in Fig. 1, but for intermediate-mass PSs. Here the first, second, and third generation of stars are represented in red, blue, and green, respectively. Panels represent: a) formation of FG stars; b) gas accumulation from winds of FG massive stars and pristine gas; c) first core-collapse SN explosions, which trigger the formation of SG stars and expel the gas that has not yet arrived at the core; d) FG and SG SN explosions; e) gas accumulation from winds of super-AGB and AGB stars of the FG and SG; f) formation of TG stars; g) present-day O-Na anticorrelation. This figure is available in color in electronic form.