Parameter space for ZAMS systems progenitors of SySt and possible SNe Ia (green filled region). The solid blue line shows the behavior of q_cut(M₁), and the solid red line that of the upper limit IFMR(M₁) / M₁ – their interception happens at M₁ ∼ 3.6 M_⊙. The solid vertical line marks the upper mass limit for C+O WDs of 6.1 M_⊙, and the dashed vertical line the lower limit of 3.3 M_⊙ for ZAMS stars progenitors of 0.8 M_⊙ WDs.