Kim A. S. Hefner Kathryn F. Jones Suh-Ryung Kim J. Richard Lundgren Fred S. Roberts (i, j) competition graphs. 241-262 1991 32 Discrete Applied Mathematics 3 http://dx.doi.org/10.1016/0166-218X(91)90002-E db/journals/dam/dam32.html#HefnerJKLR91