1. SSWL Database of Syntactic Parameters: http://sswl.railsplayground.net/
2. Perseus Software Package for Persistent Homology: http://www.sas.upenn.edu/~vnanda/perseus/
3. Chomsky, N.: Lectures on Government and Binding. Foris Publications, Dordrecht (1982)
4. Chomsky, N., Lasnik, H.: The theory of principles and parameters. In: Syntax: An International Handbook of Contemporary Research, pp. 506–569. de Gruyter (1993)
5. Baker, M.: The Atoms of Language. Basic Books, New York (2001)