Summary of our population synthesis of DHeWDs performed using the COSMIC code for metallicity Z = 0.01. The upper panel shows the SFH used in the simulation. The middle panel shows the birth rate of all DHeWDs (black histogram), as well as those among them that will become AM CVn-type systems (green histogram) or BLAPs (orange histogram). The lower panel presents the merger rate of all DHeWDs with the corresponding mass ratio (grey histogram) and those systems that will become BLAPs (orange histogram). The blue vertical line marks the age of the Universe.