| Issue |
RAIRO-Theor. Inf. Appl.
Volume 40, Number 3, July-September 2006
Word Avoidability Complexity And Morphisms (WACAM)
|
|
|---|---|---|
| Page(s) | 407 - 426 | |
| DOI | https://doi.org/10.1051/ita:2006019 | |
| Published online | 18 October 2006 | |
Well quasi-orders, unavoidable sets, and derivation systems
1
Dipartimento di Matematica,
Università di Roma “La Sapienza”
Piazzale Aldo Moro 2, 00185 Roma, Italy;
dalessan@mat.uniroma1.it
2
Dipartimento di Matematica,
Università di Roma “Tor Vergata”,
via della Ricerca Scientifica, 00133 Roma, Italy;
varricch@mat.uniroma2.it
Let I be a finite set of words and 
be the derivation relation
generated by the set of productions {ε → u | u ∈ I}.
Let 
be the set of words u such that 
.
We prove that the set I is unavoidable if and only if the relation
is a well quasi-order on the set . This result generalizes a theorem of
[Ehrenfeucht et al.,
Theor. Comput. Sci. 27 (1983) 311–332]. Further generalizations are investigated.
Mathematics Subject Classification: 68Q45 / 68R15
Key words: Well quasi-orders / context-free languages.
© EDP Sciences, 2006
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.