Geodesic
On regressive enumerations
Diskretnaya Matematika, Tome 9 (1997) no. 2, pp. 116-119 
V. L. Mikheev. On regressive enumerations. Diskretnaya Matematika, Tome 9 (1997) no. 2, pp. 116-119. http://geodesic.mathdoc.fr/item/DM_1997_9_2_a11/
@article{DM_1997_9_2_a11,
     author = {V. L. Mikheev},
     title = {On regressive enumerations},
     journal = {Diskretnaya Matematika},
     pages = {116--119},
     year = {1997},
     volume = {9},
     number = {2},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DM_1997_9_2_a11/}
}
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Voir la notice de l'article provenant de la source Math-Net.Ru

We demonstrate that any regressive set can have either exactly one or denumerable many regressive enumerations (up to equivalence), and describe the sets possessing a single regressive enumeration.