Each regular code is included in a maximal regular code
RAIRO - Theoretical Informatics and Applications - Informatique Théorique et Applications, Tome 20 (1986) no. 1, pp. 89-96. 
@article{ITA_1986__20_1_89_0,
     author = {Ehrenfeucht, A. and Rozenberg, G.},
     title = {Each regular code is included in a maximal regular code},
     journal = {RAIRO - Theoretical Informatics and Applications - Informatique Th\'eorique et Applications},
     pages = {89--96},
     publisher = {AFCET - Gauthier-Villars},
     address = {Paris},
     volume = {20},
     number = {1},
     year = {1986},
     mrnumber = {849968},
     zbl = {0609.68053},
     language = {en},
     url = {http://archive.numdam.org/item/ITA_1986__20_1_89_0/}
}
TY  - JOUR
AU  - Ehrenfeucht, A.
AU  - Rozenberg, G.
TI  - Each regular code is included in a maximal regular code
JO  - RAIRO - Theoretical Informatics and Applications - Informatique Théorique et Applications
PY  - 1986
SP  - 89
EP  - 96
VL  - 20
IS  - 1
PB  - AFCET - Gauthier-Villars
PP  - Paris
UR  - http://archive.numdam.org/item/ITA_1986__20_1_89_0/
LA  - en
ID  - ITA_1986__20_1_89_0
ER  - 
%0 Journal Article
%A Ehrenfeucht, A.
%A Rozenberg, G.
%T Each regular code is included in a maximal regular code
%J RAIRO - Theoretical Informatics and Applications - Informatique Théorique et Applications
%D 1986
%P 89-96
%V 20
%N 1
%I AFCET - Gauthier-Villars
%C Paris
%U http://archive.numdam.org/item/ITA_1986__20_1_89_0/
%G en
%F ITA_1986__20_1_89_0
Ehrenfeucht, A.; Rozenberg, G. Each regular code is included in a maximal regular code. RAIRO - Theoretical Informatics and Applications - Informatique Théorique et Applications, Tome 20 (1986) no. 1, pp. 89-96. http://archive.numdam.org/item/ITA_1986__20_1_89_0/

[BPS] J. Berstel, D. Perrin and M. P. Schutzenberger, The Theory of Codes(to appear).

[E] S. Eilenberg, Automata, Languages and Machines, Vol. A, 1974, Academic Press, New York and London. | MR | Zbl

[F] W. Feller, An Introduction to Probability Theory and its Applications, Vol. 1, 1950, J. Wiley. | MR | Zbl

[P1] D. Ed.PERRIN, Theorie des codes, L.I.T.P. Publication, Paris, 1979. | Zbl

[P2] D. Perrin, Completing Biprefix Codes, Lecture Notes in Computer Science, Vol. 140, 1982, pp. 397-406. | MR | Zbl

[P3] D. Perrin, Séries formelles et combinatoire du monoide libre, in J. Berstel Ed., Series Formelles, L.I.T.P., Paris, 1977.

[R] A. Restivo, On Codes Having no Finite Completions, in Automata, Languages and Programming, S. MICHAELSON Ed., Edinburgh University Press, 1976, pp. 38-44. | MR

[S] A. Salomaa, Formal Languages, Academic Press, London, New York, 1973. | MR | Zbl

[Sch] M. P. Schutzenberger, Une théorie algébrique du codage, Seminaire Dubreuil-Pisot, année 55-56, exp. No. 15, Inst. Henri-Poincaré, Paris, 1956. | Numdam | MR

[SM] M. P. Schutzenberger and R. S. Marcus, Full Decodable Code Word Sets, I.R.E. Trans on Inf. Theroy, Vol. 5, 1959, pp. 13-15. | MR