Results 1  10
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14
On the Weak Pigeonhole Principle
, 2001
"... We investigate the proof complexity, in (extensions of) resolution and in bounded arithmetic, of the weak pigeonhole principle and of Ramsey theorem. In particular, we link the proof complexity of these two principles. Further we give lower bounds to the width of resolution proofs and to the size of ..."
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Cited by 72 (3 self)
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We investigate the proof complexity, in (extensions of) resolution and in bounded arithmetic, of the weak pigeonhole principle and of Ramsey theorem. In particular, we link the proof complexity of these two principles. Further we give lower bounds to the width of resolution proofs and to the size of (extensions of) treelike resolution proofs of Ramsey theorem. We establish a connection between provability of WPHP in fragments of bounded arithmetic and cryptographic assumptions (the existence of oneway functions). In particular, we show that functions violating WPHP 2n n are oneway and, on the other hand, that oneway permutations give rise to functions violating PHP n+1 n , and that strongly collisionfree families of hash functions give rise to functions violating WPHP 2n n (all in suitable models of bounded arithmetic). Further we formulate few problems and conjectures; in particular, on the structured PHP (introduced here) and on the unrelativised WPHP. The symbol WPHP m n...
The provable total search problems of bounded arithmetic
, 2007
"... We give combinatorial principles GIk, based on kturn games, which are complete for the class of NP search problems provably total at the kth level T k 2 of the bounded arithmetic hierarchy and hence characterize the ∀ ˆ Σ b 1 consequences of T k 2, generalizing the results of [20]. Our argument use ..."
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Cited by 8 (4 self)
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We give combinatorial principles GIk, based on kturn games, which are complete for the class of NP search problems provably total at the kth level T k 2 of the bounded arithmetic hierarchy and hence characterize the ∀ ˆ Σ b 1 consequences of T k 2, generalizing the results of [20]. Our argument uses a translation of first order proofs into large, uniform propositional proofs in a system in which the soundness of the rules can be witnessed by polynomial time reductions between games. We show that ∀ ˆ Σ b 1(α) conservativity of of T i+1 2 (α) over T i 2(α) already implies ∀ ˆ Σ b 1(α) conservativity of T2(α) over T i 2(α). We translate this into propositional form and give a polylogarithmic width CNF GI3 such that if GI3 has small R(log) refutations then so does any polylogarithmic width CNF which has small constant depth refutations. We prove a resolution lower bound for GI3. We use our characterization to give a sufficient condition for the totality of a relativized NP search problem to be unprovable in T i 2(α) in terms of a nonlogical question about multiparty communication protocols.
Combinatorics in Bounded Arithmetics
, 2004
"... A basic aim of logic is to consider what axioms are used in proving various theorems of mathematics. This thesis will be concerned with such issues applied to a particular area of mathematics: combinatorics. We will consider two widely known groups of proof methods in combinatorics, namely, probabil ..."
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A basic aim of logic is to consider what axioms are used in proving various theorems of mathematics. This thesis will be concerned with such issues applied to a particular area of mathematics: combinatorics. We will consider two widely known groups of proof methods in combinatorics, namely, probabilistic methods and methods using linear algebra. We will consider certain applications of such methods, both of which are significant to Ramsey theory. The systems we choose to work in are various theories of bounded arithmetic. For the probabilistic method, the key point is that we use the weak pigeonhole principle to simulate the probabilistic reasoning. We formalize various applications of the ordinary probabilistic method and linearity of expectations, making partial progress on the Local Lemma. In the case of linearity of expectations, we show how to eliminate the weak pigeonhole principle by simulating the derandomization technique of “conditional probabilities.” We consider linear algebra methods applied to various set system theorems. We formalize some theorems using a linear algebra principle as an extra axiom. We also show how weaker results can be attained by giving alternative proofs that avoid linear algebra, and thus also avoid the extra axiom. We formalize upper and lower Ramsey bounds. For the lower bounds, both the probabilistic methods and the linear algebra methods are used. We provide a stratification of the various Ramsey lower bounds, showing that stronger bounds can be proved in stronger theories. A natural question is whether or not the axioms used are necessary. We provide “reversals” in a few cases, showing that the principle used to prove the theorem is in fact a consequence of the theorem (over some base theory). Thus this work can be seen as a (humble) beginning in the direction of developing the Reverse Mathematics of finite combinatorics.
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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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.
A lower bound on the size of resolution proofs of the Ramsey theorem
, 2011
"... We prove an exponential lower bound on the lengths of resolution proofs of propositions expressing the finite Ramsey theorem for pairs. Assuming that n ≥ R(k), where R(k) denotes the Ramsey number, the Ramsey theorem for pairs and two colors, n → (k) 2 2, is presented by the following unsatisfiable ..."
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We prove an exponential lower bound on the lengths of resolution proofs of propositions expressing the finite Ramsey theorem for pairs. Assuming that n ≥ R(k), where R(k) denotes the Ramsey number, the Ramsey theorem for pairs and two colors, n → (k) 2 2, is presented by the following unsatisfiable set of clauses. The variables are xij, for 1 ≤ i < j ≤ n. The clauses are ∨ i,j∈K xij and ∨ i,j∈K ¬xij, for all sets K ⊆ {1,..., n}, K  = k. The corresponding tautology will be denoted by RAM(n, k). The Ramsey theorem was proposed as a hard tautology by Krishnamurthy in [6]. He studied the tautology RAM(R(k), k) and proved a lower bound R(k)/2 on the width of resolution proofs (see also [5]). This implies an exponential lower bound on the treelike resolution proofs. Krajíček proved an exponential lower bound on this tautology by reducing the proofs of the pigeonhole principle to it, [4]. The problem with this tautology is that we do not know what is R(k). This prevent us from proving an upper bound on the proof complexity of this tautology. Therefore researchers focused on the tautology RAM(n, k) for k = ⌊ 1 log n ⌋ (all logarithms are to the base 2 in this paper). This tautology is provable in a 2 bounded depth Frege system, see [7, 4]. For this tautology, Krajíček proved an exponential lower bound on treelike resolution proofs with conjunctions of logarithmic size, [3]. The complexity of unrestricted resolution proofs with conjunctions of logarithmic size proofs of RAM(n, ⌊ 1 log n⌋) is still an open problem. An exponential lower bound on such proofs 2 would have interesting consequences in proof complexity and bounded arithmetic. In particular it would give a separation of the relativized theories T 2 2 and T 3 2 by a ∀Σb 1 sentence (see [2, 1]). In this paper we prove an exponential lower bound on unrestricted resolution proofs.
Higher complexity search problems for bounded arithmetic and
, 2010
"... a formalized nogap theorem ..."
Consistency and Gamesin Search of New Combinatorial Principles
, 2004
"... We show that a semantical interpretation of Herbrand's disjunctions can be used to obtain 2 independent sentences whose nature is more combinatorial than the nature of the usual consistency statements. Then we apply this method to Bounded Arithmetic and present 8 1 combinatorial sentence ..."
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We show that a semantical interpretation of Herbrand's disjunctions can be used to obtain 2 independent sentences whose nature is more combinatorial than the nature of the usual consistency statements. Then we apply this method to Bounded Arithmetic and present 8 1 combinatorial sentences that characterize all 8 1 sentences provable in S 2 . We use the concept of a two player game to describe these sentences.
A resolution lower bound for a principle capturing the hardness of depth1 LK
"... We introduce principles 2VR 2 and 2VR 1 which imply reflection for, respectively, the CNFs and the narrow CNFs refutable in the depth1 propositional LK system P K1. We give a polynomialsize refutation of their negations 2VR 2 and 2VR 1 in the system PK1 and show an exponential lower bound on the s ..."
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We introduce principles 2VR 2 and 2VR 1 which imply reflection for, respectively, the CNFs and the narrow CNFs refutable in the depth1 propositional LK system P K1. We give a polynomialsize refutation of their negations 2VR 2 and 2VR 1 in the system PK1 and show an exponential lower bound on the size of their resolution refutations. We conjecture that they have no small Res(log) refutations; this would be the first such lower bound for a principle with bounded depth refutations. We also show that if any CNF with a small PK1 refutation is exponentially hard for Res(log) then 2VR 2 is as well. 1.