Title
An extension of the omega-rule.
Abstract
The $$Omega $$Ω-rule was introduced by W. Buchholz to give an ordinal-free proof of cut-elimination for a subsystem of analysis with $$Pi ^{1}_{1}$$?11-comprehension. W. Buchholzu0027s proof provides cut-free derivations by familiar rules only for arithmetical sequents. When second-order quantifiers are present, they are introduced by the $$Omega $$Ω-rule and some residual cuts are not eliminated. In the present paper, we introduce an extension of the $$Omega $$Ω-rule and prove the complete cut-elimination by the same method as W. Buchholz: any derivation of arbitrary sequent is transformed into its cut-free derivation by the standard rules (with induction replaced by the $$omega $$?-rule). In fact we treat the subsystem of $$Pi ^{1}_{1}$$?11-CA (of the same strength as $$ID_{1}$$ID1) that W. Buchholz used for his explanation of G. Takeutiu0027s finite reductions. Extension to full $$Pi ^{1}_{1}$$?11-CA is planned for another paper.
Year
DOI
Venue
2016
10.1007/s00153-016-0482-y
Arch. Math. Log.
Keywords
Field
DocType
Cut-elimination, Infinitary proof theory, Ordinal analysis, 03F05, 03F35
Discrete mathematics,Combinatorics,Arithmetic function,Ordinal analysis,Omega,Sequent,Mathematics
Journal
Volume
Issue
ISSN
55
3-4
1432-0665
Citations 
PageRank 
References 
2
0.44
4
Authors
2
Name
Order
Citations
PageRank
Ryota Akiyoshi141.90
Grigori Mints223572.76