2-Packing of a graph

2-Packing of a graph --- 2-упаковка графа.

A subset [math]\displaystyle{ A }[/math] of [math]\displaystyle{ G }[/math] is called a 2-packing of [math]\displaystyle{ G }[/math] if the closed neighborhoods of any two distinct vertices of [math]\displaystyle{ A }[/math] are disjoint. The 2-packing number of [math]\displaystyle{ G }[/math] is the maximum cardinality, [math]\displaystyle{ \rho(G) }[/math], of 2-packing of [math]\displaystyle{ G }[/math].