Cactus

Cactus --- кактус, дерево Хусими.

A graph [math]\displaystyle{ G }[/math] is a сactus if every its edge is a part of at most one cycle in [math]\displaystyle{ G }[/math]. Cactus graphs are outerplanar since they cannot contain [math]\displaystyle{ K_{4} }[/math] or [math]\displaystyle{ K_{2,3} }[/math] as a minor. Cactus graphs have treewidth [math]\displaystyle{ \leq 2 }[/math].