Top: two examples of high-redshift CPs. in TNG100, progenitors of a FR (left) and of a SR (right). Both CPs are shown edge-on and have rather disky shapes. Physical parameters are reported in the figure. Center: mass functions of the entire sample of TNG ETGs (gray dashed), of the ETGs descending from a compact progenitor (magenta dashed), and of the ETGs with “surviving compact progenitor cores” (CP-cores, magenta solid line). The distribution of galaxies whose main progenitors were never compact is also shown (gray solid line). Bottom: fraction of galaxies, in mass bins, with compact progenitors, with surviving CP-cores, and with surviving CP-cores for SRs only and split by accretion class. The fraction of galaxies with CPs is a strong function of stellar mass but the fraction of objects with surviving CP-cores is nearly constant at ∼20% at M_* ≳ 10^10.7 M_⊙, and decreases at lower masses.