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(en) Thomas S. E. Maibaum, « A Generalized Approach to Formal Languages », J. Computer and System Sciences, vol. 8, no 3, , p. 409–439 (DOI10.1016/s0022-0000(74)80031-0, lire en ligne).
(en) Takafumi Hayashi, « On Derivation Trees of Indexed Grammars - An Extension of the uvxyz Theorem », Publication of the Research Institute for Mathematical Sciences, vol. 9, no 1, , p. 61–92 (DOI10.2977/prims/1195192738, lire en ligne)
ems-ph.org
(en) Takafumi Hayashi, « On Derivation Trees of Indexed Grammars - An Extension of the uvxyz Theorem », Publication of the Research Institute for Mathematical Sciences, vol. 9, no 1, , p. 61–92 (DOI10.2977/prims/1195192738, lire en ligne)
(en) Thomas S. E. Maibaum, « A Generalized Approach to Formal Languages », J. Computer and System Sciences, vol. 8, no 3, , p. 409–439 (DOI10.1016/s0022-0000(74)80031-0, lire en ligne).