1. A Theorem on Boolean Matrices;Warshall;JACM,1962
2. A Transitive Closure Algorithm;Purdom,1968
3. M. Fischer and A. Meyer, private correspondence.
4. On Efficient Construction of Transitive Closure of Directed Graphs;Atlazarov;Soviet Mathematics-Doklady,1970
5. Gaussian Elimination is not Optimal;Strassen;Numerische Mathematique,1969