TY - CONF A1 - Zheng, Xizhong T1 - On the hierarchy of Delta_02-numbers Y1 - 2005 UR - https://opus4.kobv.de/opus4-UBICO/frontdoor/index/index/docId/2029 UR - http://www.informatik.uni-trier.de/Reports/TR-08-2004/rnc6_15_zheng.pdf ER -