Before revision: An \alpha-additive spanner of an undirected graph G =(V, E)  is a subgraph H such that the distance between any two vertices in G is stretched by no more than an additive factor of \alpha. It is previously known that unweighted graphshave 2-, 4-, and 6-additive spanners containing (n^{3/2), } (n^{7/5), and O(n^{4/3}) edges, respectively.
After revision: An \alpha-additive spanner of an undirected graph G =(V, E) is a subgraph H (n^{3/2), } (n^{7/5), and O(n^{4/3}) edges, respectively.