M. Blaze, J. Feigenbaum, and M. Strauss. FC 1998: Proceedings of the Second International Conference on Financial Cryptography, page 254--274. London, UK, Springer-Verlag, (1998)
F. Strauß, S. Hügel, K. Winter, and B. Schinzel. Software-Ergonomie, volume 45 of Berichte des German Chapter of the ACM, page 369-382. Teubner, (1995)