Gazdar, Gerald (1988). "Applicability of Indexed Grammars to Natural Languages". In Reyle, U.; Rohrer, C. (eds.). Natural Language Parsing and Linguistic Theories. Studies in Linguistics and Philosophy. Vol. 35. Springer Netherlands. pp. 69–94. doi:10.1007/978-94-009-1337-0_3. ISBN978-94-009-1337-0.
Fischer, Michael J. (October 1968). "Grammars with macro-like productions". 9th Annual Symposium on Switching and Automata Theory (Swat 1968). pp. 131–142. doi:10.1109/SWAT.1968.12.