The classical concept of Shannon capacity of undirected graphs
was extended by Gargano, Körner, and Vaccaro to digraphs in the early 1990s, and termed Sperner capacity. Shannon, in his seminal work, determined the capacities for all isomorphism classes of undirected graphs with up to five vertices, except for the 5-cycle, which was finally settled by Lovász in 1979.
The work of Shannon is here paralleled for digraphs; the Sperner capacity is determined for all but 8 of the 9846 isomorphism classes of digraphs with at most 5 vertices.
Mathematics Subject Classification: Primary: 94A24; Secondary: 05C20.