1. Alther, R., Cherakov, L., and Becker, C. Virtual spaces: enabling immersive collaborative enterprise: part 2: implementation and lessons learned. IBM Developer Works, Armonk, NY, 2009. .
2. Existence of an equilibrium for a competitive economy;Arrow;Econometrica,1954
3. Bentham, J. An Introduction to the Principles of Morals and Legislation, digital edition, 1781. .
4. Offdigital: why money has always been virtual;Budd;City,2000
5. Cherbakov, L., Brunner, R., Smart, R., and Lu, C. Virtual spaces: enabling immersive collaborative enterprise, part 1: introduction to the opportunities and technologies. IBM Developer Works, Armonk, NY, 2009. .