We prove that for each positive integer the finite commutative language possesses a test set of size at most Moreover, it is shown that each test set for has at least elements. The result is then generalized to commutative languages containing a word such that (i) and (ii) each symbol occurs at least twice in if it occurs at least twice in some word of : each such possesses a test set of size , where . The considerations rest on the analysis of some basic types of word equations.
@article{ITA_2001__35_5_453_0, author = {Holub, \v St\v ep\'an and Kortelainen, Juha}, title = {Linear size test sets for certain commutative languages}, journal = {RAIRO - Theoretical Informatics and Applications - Informatique Th\'eorique et Applications}, volume = {35}, year = {2001}, pages = {453-475}, mrnumber = {1908866}, zbl = {1010.68103}, language = {en}, url = {http://dml.mathdoc.fr/item/ITA_2001__35_5_453_0} }
Holub, Štěpán; Kortelainen, Juha. Linear size test sets for certain commutative languages. RAIRO - Theoretical Informatics and Applications - Informatique Théorique et Applications, Tome 35 (2001) pp. 453-475. http://gdmltest.u-ga.fr/item/ITA_2001__35_5_453_0/
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