References
[Garey et al., 1979]
Garey, Michael R. and Johnson, David S. Computers and intractability: a guide to the theory of NP-completeness. New York; Oxford: Freeman; 1979. ISBN: 0-7167-1044-7.
Cyberspace geography visualization - 15 October 1995
Luc Girardin, The Graduate Institute of International Studies