Paper Title
A Constructive Characterization of Trees with the Same Distance-2 Domination Number

Abstract
The distance between two vertices u and v in a graph G equalsthe length of a shortest path from u to v . A set D of verticesis distance-2 dominating if every vertex not belonging to D is atdistance at most two of a vertex in D .The distance-2 domination number of a graph G , denoted by ( ) 2  G , is the minimum cardinality of adistance-2 dominating setinG .Notethat in general to determine the number ( ) 2  G in a graph Gis NP-complete even if G is bipartite [4]. Here we focus on the trees. For n  1 , let (n) be the set of trees T satisfying (T)  n 2  . In thispaper, we provide a constructive characterization of (n) for all n  1.