@article{105653, author = {Anton\'\i n Sochor}, title = {Real classes in the ultrapower of hereditarily finite sets}, journal = {Commentationes Mathematicae Universitatis Carolinae}, volume = {016}, year = {1975}, pages = {637-640}, zbl = {0327.02047}, mrnumber = {0389588}, language = {en}, url = {http://dml.mathdoc.fr/item/105653} }
Sochor, Antonín. Real classes in the ultrapower of hereditarily finite sets. Commentationes Mathematicae Universitatis Carolinae, Tome 016 (1975) pp. 637-640. http://gdmltest.u-ga.fr/item/105653/
The theory of semisets, North-Holland P. C. and Academia, Prague, 1972. (1972) | MR 0444473
Matematika v alternativní teorii množin, (Mathematics in the Alternative theory of sets), manuscript.