Levelt, Willem J. M. Language Production Group Levelt, MPI for Psycholinguistics, Max Planck Society; University of Nijmegen;
Levelt_Formal_Grammars_1978.pdf (Publisher version), 2MB
Levelt, W. J. M. (1976). Formal grammars and the natural language user: A review. In A. Marzollo (Ed.), Topics in artificial intelligence (pp. 226-290). Vienna: Springer.