# On the Strong Metric Dimension of directed co-graphs

Let G be a strongly connected directed graph and u,v,w∈ V(G) be three vertices. Then w strongly resolves u to v if there is a shortest u-w-path containing v or a shortest w-v-path containing u. A set R⊆ V(G) of vertices is a strong resolving set for a directed graph G if for every pair of vertices u,v∈ V(G) there is at least one vertex in R that strongly resolves u to v and at least one vertex in R that strongly resolves v to u. The distances of the vertices of G to and from the vertices of a strong resolving set R uniquely define the connectivity structure of the graph. The Strong Metric Dimension of a directed graph G is the size of a smallest strong resolving set for G. The decision problem Strong Metric Dimension is the question whether G has a strong resolving set of size at most r, for a given directed graph G and a given number r. In this paper we study undirected and directed co-graphs and introduce linear time algorithms for Strong Metric Dimension. These algorithms can also compute strong resolving sets for co-graphs in linear time.