1. R.J. Anderson and E.W. Mayr “Approximating P-complete problems,” Tech Report, Stanford University, 1986.
2. J.L. Bentley, T. Ottmann, P. Widmayer, “The Complexity of Manipulating Hierarchically Defined set of Intervals,” Advances in Computing Research, ed. F.P. Preparata Vol. 1, (1983), pp. 127–158.
3. A. Condon, J. Feigenbaum, C. Lund and P. Shor, “Probabilistically Checkable Debate Systems and Approximation Algorithms for PSPACE-Hard Functions”, to appear in Proc. 25th ACM Symposium on Theory of Computing, 1993.
4. H. Galperin and A. Wigderson, “Succinct Representation of Graphs,” Information and Control, Vol. 56, 1983, pp. 183–198.
5. M.R. Garey, D.S. Johnson, Computers and Intractability. A Guide to the Theory of NP-Completeness, Freeman, San Francisco CA, 1979.