* [[Frank Harary|Harary, F.]] and Read, R., "Is the Null Graph a Pointless Concept?", ''Graphs and Combinatorics Conference'', George Washington University, Springer-Verlag, New York, NY, 1973. | * [[Frank Harary|Harary, F.]] and Read, R., "Is the Null Graph a Pointless Concept?", ''Graphs and Combinatorics Conference'', George Washington University, Springer-Verlag, New York, NY, 1973. |