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June 2008 Generic complexity of undecidable problems
Alexei G. Myasnikov, Alexander N. Rybalov
J. Symbolic Logic 73(2): 656-673 (June 2008). DOI: 10.2178/jsl/1208359065


In this paper we study generic complexity of undecidable problems. It turns out that some classical undecidable problems are, in fact, strongly undecidable, i.e., they are undecidable on every strongly generic subset of inputs. For instance, the classical Halting Problem is strongly undecidable. Moreover, we prove an analog of the Rice theorem for strongly undecidable problems, which provides plenty of examples of strongly undecidable problems. Then we show that there are natural super-undecidable problems, i.e., problem which are undecidable on every generic (not only strongly generic) subset of inputs. In particular, there are finitely presented semigroups with super-undecidable word problem. To construct strongly- and super-undecidable problems we introduce a method of generic amplification (an analog of the amplification in complexity theory). Finally, we construct absolutely undecidable problems, which stay undecidable on every non-negligible set of inputs. Their construction rests on generic immune sets.


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Alexei G. Myasnikov. Alexander N. Rybalov. "Generic complexity of undecidable problems." J. Symbolic Logic 73 (2) 656 - 673, June 2008.


Published: June 2008
First available in Project Euclid: 16 April 2008

zbMATH: 1140.03025
MathSciNet: MR2414470
Digital Object Identifier: 10.2178/jsl/1208359065

Rights: Copyright © 2008 Association for Symbolic Logic


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Vol.73 • No. 2 • June 2008
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