Indexed languages are interesting in computational linguistics because they
are the least class of languages in the Chomsky hierarchy that has not been
shown not to be adequate to describe the string set of natural language
sentences. We here define a class of unification grammars that exactly describe
the class of indexed languages.Comment: 16 pages uuencodet gnu-compressed PostScript format. Also in
  Proceedings of the 10th Nordic Conference of Computational Linguistics,
  NODALIDA-95, Helsinki, 199