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.
After revision: An \alpha-additive spanner of an undirected graph G =(V, E)spanner 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.