Example of residues discarded (a) or included (b) in a R-HET after visual analysis. a. Two identical residues (ARG) belonging to two aligned proteins (protein A and B), which are clearly not correctly structurally aligned, though they fall in the same cell of the HET. The 3D multiple alignment grid is represented in green as a 2D grid. Structure segments of protein A and B are reported in red and black, respectively. This pair of residues is discarded after visual analysis. b. Two different residues (ARG and ASP) belonging to two aligned proteins (protein A and B), which clearly correspond though they do not fall in the same cell of the HET. This pair of residues is included in the R-HET after visual inspection.