@inproceedings{ZhengRettingerGengler2005, author = {Xizhong Zheng and Robert Rettinger and Romain Gengler}, title = {Ershov's hierarchy of real numbers}, booktitle = {Mathematical foundations of computer science 2003, 28th international symposium MFCS, Bratislava, Slovakia, August 25 - 29, 2003}, editor = {Branislav Rovan}, pages = {681 -- 690}, year = {2005}, }