sentences:  Forbidden graph characterization
  
  In graph theory, a branch of mathematics, many important families of graphs can be described by a finite set of individual graphs
  that do not belong to the family and further exclude all graphs from the family which contain any of these forbidden graphs as (induced) subgraph or minor.A prototypical example of this phenomenon is Kuratowski's theorem, which states that a graph is planar (can be drawn without crossings in the plane) if and only if it does not contain either of two forbidden graphs, the complete graph "K"5 and the complete bipartite graph "K"3,3.