Ladder

Ladder --- лестница.

The ladder graphs (or ladders), are the graphs [math]\displaystyle{ P_{2} \times P_{n} }[/math] of order [math]\displaystyle{ 2n }[/math]. The [math]\displaystyle{ n }[/math] copies of [math]\displaystyle{ P_{2} }[/math] that connect the two copies of [math]\displaystyle{ P_{n} }[/math] are called rungs. Since these graphs are also called [math]\displaystyle{ (2,n) }[/math]-meshes, we denote them by [math]\displaystyle{ M_{2,n} }[/math].