In parallel β-sheet structure, if two atoms C and C are adjacent in two hydrogen-bonded β-strands, then they do "not" hydrogen bond to each other; rather, one residue forms hydrogen bonds to the residues that flank the other (but not vice versa). For example, residue "i" may form hydrogen bonds to residues "j" − 1 and "j" + 1; this is known as a wide pair of hydrogen bonds. By contrast, residue "j" may hydrogen-bond to different residues altogether, or to none at all.