P. Bottoni, G. Mauri, and P. Mussio. Recent Topics in Mathematical and Computational Linguistics, page 25-45. Editura Academiei Române, Bucuresti, (2000)
P. Bottoni, G. Mauri, and P. Mussio. Grammatical Models of Multi-Agent Systems, volume 8 of Topics in Computer Mathematics, page 226-246. Gordon and Breach Science Publishers, (1999)