1. Becker, R.A., Chambers, J.M., Wilks, A.R.: The New S Language: A Programming Environment for Data Analysis and Graphics. Wadsworth & Brooks/Cole, Pacific Grove (1988)
2. Bentley, J.L., Mallows, C.L.: Problem submitted to American Mathematical Monthly (2005)
3. Bishop, M., Klein, D.V.: Improving system security via proactive password checking. Computers and Security 14(3), 233–249 (1995)
4. Cachin, C.: Entropy measures and unconditional security in cryptography, Ph.D. Thesis, ETH Zurich (1997)
5. Chew, M., Baird, H.S.: BaffleText: a Human Interactive Proof. In: Proceedings IS&T/SPI Document Recognition and Retrieval X Conference (ER&R 2003), Santa Clara, CA (January 2003)