Geodesic
Proper classes corresponding to the functors $n\cdot\operatorname{Ext}$
Vestnik Moskovskogo universiteta. Matematika, mehanika, no. 2 (1983), pp. 22-24 
S. N. Fedin. Proper classes corresponding to the functors $n\cdot\operatorname{Ext}$. Vestnik Moskovskogo universiteta. Matematika, mehanika, no. 2 (1983), pp. 22-24. http://geodesic.mathdoc.fr/item/VMUMM_1983_2_a4/
@article{VMUMM_1983_2_a4,
     author = {S. N. Fedin},
     title = {Proper classes corresponding to the functors $n\cdot\operatorname{Ext}$},
     journal = {Vestnik Moskovskogo universiteta. Matematika, mehanika},
     pages = {22--24},
     year = {1983},
     number = {2},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/VMUMM_1983_2_a4/}
}
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Voir la notice de l'article provenant de la source Math-Net.Ru

We prove that for all $n>0$ the functor $n\cdot\operatorname{Ext}$ defines a proper clasp. We establish main properties of such classes.