The logarithmic alternation hierarchy collapses: \(A\Sigma _ 2^{{\mathcal L}}=A\Pi_ 2^{{\mathcal L}}\). (English) Zbl 0668.68055

It is shown that the second level of the logarithmic space hierarchy is closed under complementation, i.e., this hierarchy “collapses” to its second level. The result is proved by considering the Hausdorff closure of NL, and also the Boolean NL and NP hierarchy.
A more recent result by Immerman shows that the results reported in the present paper are not the strongest possible ones: Actually, NL is closed under complementation, i.e. the logarithmic alternation hierarchy collapses to its first level.
Reviewer: U.Schöning


68Q05 Models of computation (Turing machines, etc.) (MSC2010)
68Q25 Analysis of algorithms and problem complexity
03D15 Complexity of computation (including implicit computational complexity)
Full Text: DOI


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