Graph theory and tree.
Introduction : Graph theory may be said to have its beginning in 1736 when Euler considered the (general case of the) Konigsberg bridge problem. Does there exist a walk crossing each of the seven bridges of Konigsberg exactly once? It took 200 years before the first book on graph theory was written. This was " Theorie der endlichen und unendlichen Graphen " by koing in 1936 .Since,then graph theory has developed into an extensive and popular branch of mathematics,which has been applied to many problems in mathematics, computer science and other scientific and not-s-scientific areas. There are no standard notations for graph theoretical objects. This is natural because the names one uses for the objects reflect the applications. Thus, for instance, if we consider a communication network (say, for email) as a graph, the computers taking part in this network, are called nodes rather than vertices or points.On the other hand, other names are used for molecular structures