Inverse mapping results. Initial conditions for stars A (circles) and B (stars) reproduce the observed parameters (R, L, Z/X)_obs at given ages. Colors indicate the ages, as shown in the legend. Colored lines show the initial chemical compositions obtained by accounting for observation errors ±Δ(Z/X). The black line shows the common initial conditions (Y_ini, Z_ini) for which the stars achieve the observed values (R, L, Z/X ± Δ(Z/X))_obs at ages from 7.801 to 7.826 Ga.