Carbon isotope ratios ¹²C/¹³C of sample stars in different evolutionary stages (RGB left panels, HB right panels) against different stellar parameters. Additionally, stars are color-coded by their A(Li), with different symbols indicating Li upper limits (circles) and measurements (squares). The A(Li) range of the color bar is selected to make variations of most of the sample stars clearer, but A(Li) of HIP 3137 exceeds the top value of this range.