1. Apt, K.: Principles of Constraint Programming. Cambridge University Press, New York (2003)
2. Dechter, R.: Constraint processing. Elsevier Morgan Kaufmann (2003)
3. Demassey, S.: Global Constraint Catalog, 05 June 2016. http://sofdem.github.io/gccat/ . Accessed 24 Oct 2017
4. German Federal Institute for Occupational Safety and Health (BAuA) - Design of night and shift work (2013). http://www.baua.de/ . Accessed 10 May 2017
5. German working time law from 6. June 1994, (BGBl.IS.1170,1171), last updates by Art. 3 para. 6 of the Law of 20 April 2013 (BGBl.IS.868) (1994). http://www.gesetze-im-internet.de/arbzg . Accessed 10 May 2017