Surface abundance of ³He (in mass fraction, top-left panel), ¹²C/¹³C (top-right panel), [C/Fe] (bottom-left panel), and [N/Fe] (bottom-right panel) as a function of stellar mass for synthetic thin disc computed with the BGM. Stars have been selected to be in the clump according to their ΔΠ_{ℓ = 1}. The colour code represents the metallicity of stars. Simulations including or not the effects of thermohaline instability are represented by colour-dots and crosses respectively.