Forbidden subgraph --- запрещенный подграф.
1. If are graphs, then a graph is said to be -free if contains no copy of any of the graphs as an induced subgraph; the graphs will be also referred to in this context as forbidden subgraphs.
2. A cf-graph with the initial node has a forbidden subgraph if there exist distinct nodes , and and simple paths , , , , , where denotes a path from to , that do not intersect on internal nodes.