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A labeled graph 
 is a finite series of Vertices 
 with a set of
Edges 
 of 2-Subsets of 
.  Given a Vertex set
, 2, ..., 
, the number of labeled graphs is given by 
. Two graphs 
 and 
 with
Vertices 
 are said to be Isomorphic if
there is a Permutation 
 of 
 such that 
 is in the set of Edges 
Iff 
 is in the set of Edges 
.
See also Connected Graph, Graceful Graph, Graph (Graph Theory), Harmonious Graph, Magic Graph, Taylor's Condition, Weighted Tree
References
Cahit, I.  ``Homepage for the Graph Labelling Problems and New Results.''
  http://193.140.42.134/~cahit/CORDIAL.html.
 
Gallian, J. A.  ``Graph Labelling.''  Elec. J. Combin. DS6, 1-43, Mar. 5, 1998.
  http://www.combinatorics.org/Surveys/.