Abundance-to-iron ratios of Li, O, Na, Mg, and K in the sample of TO stars, shown in various abundance-abundance planes. Colors on the left and right sides of the symbols correspond to the quality (symbols denoting different quality classes are shown in the top-left panel) of spectral lines used to determine abundances of the light elements in a given star plotted on the y and x axes, respectively (see Sect. 2.3.2 for details). The values of two-tailed probabilities, p, computed using Pearson’s parametric correlation coefficients (with and without abundance errors, p ^witherrors and p ^{withouterrors}, respectively), Spearman’s, and Kendall’s non-parametric rank-order correlation coefficients are given in the corresponding panels (see Sect. 3.2).