TY  - JOUR
AU  - Topi Urponen
TI  - On regular expressions over one letter and on commutative languages
JO  - Annales Fennici Mathematici
PY  - 1972
VL  - 501-520
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/articles/10.5186/aasfm.1972.517/
DO  - 10.5186/aasfm.1972.517
LA  - en
ID  - AFM_1972_501-520_a3
ER  -