Observed [α/Fe] vs. [Fe/H] abundance ratios of the APOKASC sample (grey points) presented by Silva Aguirre et al. (2018) compared with the two-infall chemical evolution model characterised by τ₁ = 0.1 Gyr, τ₂ = 8 Gyr, σ₂ = 64 M_⊙ pc⁻², σ₂/σ₁ = 4, and ν = 1.3 Gyr⁻¹. The three yellow points clearly show that the predicted chemical evolution curve is multi-valued in this plane (they exhibit three different [α/Fe] values for the same [Fe/H] abundance ratio).