Bondy--Chvtal closure operation

Bondy--Chv\'{a}tal closure operation --- операция замыкания Бонди-Хватала.

Given a graph of order [math]\displaystyle{ n }[/math], repeat the following operation as long as possible. For each pair of nonadjacent vertices [math]\displaystyle{ a }[/math] and [math]\displaystyle{ b }[/math], if [math]\displaystyle{ d(a) + d(b) \geq n }[/math], then add the edge [math]\displaystyle{ ab }[/math] to [math]\displaystyle{ G }[/math]. We denote by [math]\displaystyle{ cl(G) }[/math] the resulting graph and call it the Bondy--Chv\'{atal closure} of [math]\displaystyle{ G }[/math].