One of the simplest context-sensitive but not context-free languages is : the language of all strings consisting of occurrences of the symbol "a", then "b"s, then "c"s (abc, , , etc.). A superset of this language, called the Bach language, is defined as the set of all strings where "a", "b" and "c" (or any other set of three symbols) occurs equally often (, , etc.) and is also context-sensitive.Bach, E. (1981). "Discontinuous constituents in generalized categorial grammars" . NELS, vol. 11, pp. 1–12.Joshi, A.; Vijay-Shanker, K.; and Weir, D. (1991). "The convergence of mildly context-sensitive grammar formalisms". In: Sells, P., Shieber, S.M. and Wasow, T. (Editors). Foundational Issues in Natural Language Processing. Cambridge MA: Bradford.
one of the simplest context-sensitive but not context-free languages is  the language of all strings consisting of occurrences of the symbol "a" then "b"s then "c"s (abc   etc) a superset of this language called the bach language is defined as the set of all strings where "a" "b" and "c" (or any other set of three symbols) occurs equally often (  etc) and is also context-sensitivebach e (1981) "discontinuous constituents in generalized categorial grammars"  nels vol 11 pp 1–12joshi a; vijay-shanker k; and weir d (1991) "the convergence of mildly context-sensitive grammar formalisms" in sells p shieber sm and wasow t (editors) foundational issues in natural language processing cambridge ma bradford