There is no complete axiom system for shuffle expressions

Issue		RAIRO-Theor. Inf. Appl. Volume 33, Number 3, May-June 1999


Page(s)		271 - 277
DOI		10.1051/ita:1999117

DOI: 10.1051/ita:1999117

Theoret. Informatics Appl. 33 (1999) 271-277

There is no complete axiom system for shuffle expressions

A. Szepietowski
Mathematical Institute, University of Gdansk, ul. Wita Stwosza 57, 80-952 Gdansk, Poland;(matszp@halina.univ.gda.pl)

Received January, 1999. Accepted March, 1999.

Abstract: In this paper we show that neither the set of all valid equations between shuffle expressions nor the set of schemas of valid equations is recursively enumerable. Thus, neither of the sets can be recursively generated by any axiom system.

AMS Subject Classification: 68Q45.

Communicated by: Ch. Choffrut.

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