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Polynomial Local Search in the Polynomial Hierarchy and Witnessing in Fragments of Bounded Arithmetic
, 2008
"... The complexity class of Π p kpolynomial local search (PLS) problems is introduced and is used to give new witnessing theorems for fragments of bounded arithmetic. For 1 ≤ i ≤ k + 1, the Σ p idefinable functions of T k+1 2 are characterized in terms of Π p kPLS problems. These Π p kPLS problems c ..."
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Cited by 8 (3 self)
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The complexity class of Π p kpolynomial local search (PLS) problems is introduced and is used to give new witnessing theorems for fragments of bounded arithmetic. For 1 ≤ i ≤ k + 1, the Σ p idefinable functions of T k+1 2 are characterized in terms of Π p kPLS problems. These Π p kPLS problems can be defined in a weak base theory such as S1 2, and proved to be total in T k+1 2. Furthermore, the Π p kPLS definitions can be skolemized with simple polynomial time functions, and the witnessing theorem itself can be formalized, and skolemized, in a weak base theory. We introduce a new ∀Σb 1(α)principle that is conjectured to separate T k 2 (α) and T k+1 2 (α). 1
Alternating minima and maxima, Nash equilibria and Bounded Arithmetic
, 2009
"... We show that the least number principle for strict Σb k formulas can be characterized by the existence of alternating minima and maxima of length k. We show simple prenex forms of these formulas whose herbrandizations (by polynomial time functions) are ∀ ˆ Σb 1 formulas that characterize ∀ ˆ Σb 1 th ..."
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Cited by 5 (2 self)
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We show that the least number principle for strict Σb k formulas can be characterized by the existence of alternating minima and maxima of length k. We show simple prenex forms of these formulas whose herbrandizations (by polynomial time functions) are ∀ ˆ Σb 1 formulas that characterize ∀ ˆ Σb 1 theorems of the levels T k 2 of the Bounded Arithmetic Hierarchy, and we derive from this another characterization, in terms of a search problem about finding pure Nash equilibria in kturn games.
Fragments of Approximate Counting
, 2012
"... We study the longstanding open problem of giving ∀Σ b 1 separations for fragments of bounded arithmetic in the relativized setting. Rather than considering the usual fragments defined by the amount of induction they allow, we study Jeˇrábek’s theories for approximate counting and their subtheories. ..."
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Cited by 1 (0 self)
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We study the longstanding open problem of giving ∀Σ b 1 separations for fragments of bounded arithmetic in the relativized setting. Rather than considering the usual fragments defined by the amount of induction they allow, we study Jeˇrábek’s theories for approximate counting and their subtheories. We show that the ∀Σ b 1 Herbrandized ordering principle is unprovable in a fragment of bounded arithmetic that includes the injective weak pigeonhole principle for polynomial time functions, and also in a fragment that includes the surjective weak pigeonhole principle for FP NP functions. We further give new propositional translations, in terms of random resolution refutations, for the consequences of T 1 2 augmented with the surjective weak pigeonhole principle for polynomial time functions.
Higher complexity search problems for bounded arithmetic and
, 2010
"... a formalized nogap theorem ..."