Klaus Reinhardt, Eric Allender

We show that in the context of nonuniform complexity,

nondeterministic logarithmic space bounded computation can be made

unambiguous. An analogous result holds for the class of problems

reducible to context-free languages. In terms of complexity classes,

this can be stated as:

NL/poly = UL/poly

LogCFL/poly ...
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Eric Allender, Klaus-Joern Lange

We show that every language accepted by a nondeterministic auxiliary pushdown automaton in polynomial time (that is, every language in SAC$^1$ = LogCFL) can be accepted by a symmetric auxiliary pushdown automaton in polynomial time.

Shiva Kintali

A celebrated theorem of Savitch states that NSPACE(S) is contained DSPACE(S^2). In particular, Savitch gave a deterministic algorithm to solve ST-CONNECTIVITY (an NL-complete problem) using O(log^2{n}) space, implying NL is in DSPACE(log^2{n}). While Savitchâ€™s theorem itself has not been improved in the last four decades, studying the space complexity of ... more >>>

Dieter van Melkebeek, Gautam Prakriya

We study the possibility of deterministic and randomness-efficient isolation in space-bounded models of computation: Can one efficiently reduce instances of computational problems to equivalent instances that have at most one solution? We present results for the NL-complete problem of reachability on digraphs, and for the LogCFL-complete problem of certifying acceptance ... more >>>