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- Johannes Köbler, Osamu Watanabe
- ICALP
- 1995

We show that if a self-reducible set has polynomial-size circuits, then it is low for the probabilistic class ZPP(NP). As a consequence we get a deeper collapse of the polynomial-time hierarchy PH to ZPP(NP) under the assumption that NP has polynomial-size circuits. This improves on the well-known result of Karp, Lipton, and Sipser [KL80] stating a collapse… (More)

- Johannes Köbler, Uwe Schöning, Klaus W. Wagner
- ITA
- 1987

- Birgit Jenner, Johannes Köbler, Pierre McKenzie, Jacobo Torán
- J. Comput. Syst. Sci.
- 2003

- Johannes Köbler, Jochen Messner, Jacobo Torán
- Inf. Comput.
- 2003

imply complete sets for promise classes Johannes Köblery, Jochen Messnerz and Jacobo Toránz yInstitut für Informatik, Humboldt-Universität zu Berlin, 10099 Berlin, Germany, zAbt. Theoretische Informatik, Universität Ulm Oberer Eselsberg, 89069 Ulm, Germany, A polynomial time computable function h : ! whose range is a set L is called a proof system for L. In… (More)

- Vikraman Arvind, Johannes Köbler
- Theor. Comput. Sci.
- 2001

In this paper we extend a key result of Nisan and Wigderson NW94] to the nondeterministic setting: for all > 0 we show that if there is a language in E = DTIME(2 O(n)) that is hard to approximate by nondeterministic circuits of size 2 n , then there is a pseudorandom generator that can be used to derandomize BP NP (in symbols, BP NP = NP). By applying this… (More)

- Johannes Köbler, Uwe Schöning, Seinosuke Toda, Jacobo Torán
- J. Comput. Syst. Sci.
- 1989

The intractability of the complexity class NP has motivated the study of subclasses that arise when certain restrictions on the definition of NP are imposed. For example, the study of sparse sets in NP [Ma82], the study of the probabilistic classes whithin NP [Gi77], and the study of low sets in NP for the classes in the polynomial time hierarchy [Sc83],… (More)

- Johannes Köbler, Thomas Thierauf
- SIAM J. Comput.
- 1994

We consider uniform subclasses of the nonuniform complexity classes de ned by Karp and Lipton via the notion of advice functions These subclasses are obtained by restricting the complexity of computing correct advice We also investigate the e ect of allowing advice functions of limited complexity to depend on the input rather than on the input s length… (More)

- Johannes Köbler, Seinosuke Toda
- Mathematical systems theory
- 1993

We investigate the computational power of the new counting class ModP which generalizes the classes Mod p P,p prime. We show that ModP is polynomialtime truth-table equivalent in power to #P and that ModP is contained in the class AmpMP. As a consequence, the classes PP, ModP, and AmpMP are all Turing equivalent, and thus AmpMP and ModP are not low for MP… (More)

- Johannes Köbler, Sebastian Kuhnert, Oleg Verbitsky
- J. Discrete Algorithms
- 2012

We present a logspace algorithm that constructs a canonical intersection model for a given proper circular-arc graph, where canonical means that models of isomorphic graphs are equal. This implies that the recognition and the isomorphism problems for this class of graphs are solvable in logspace. For a broader class of concave-round graphs, that still… (More)

- Vikraman Arvind, Bireswar Das, Johannes Köbler, Seinosuke Toda
- Algorithmica
- 2009

We describe a fixed parameter tractable (fpt) algorithm for Colored Hypergraph Isomorphism, denoted CHI, which has running time (2 b N) O(1), where the parameter b is the maximum size of the color classes of the given hypergraphs and N is the input size. We also describe an fpt algorithm for a parameterized coset intersection problem that is used as a… (More)