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Logic seminar

usually takes place each Monday at 13:30 temporarily on Zoom starting at 15:30, normally in IM, rear building, ground floor
Chair: Pavel Pudlak, Neil Thapen, Jan Krajíček
More information on the old seminar web page. The programme is announced via the mailing list.

TBA

Tin Lok Wong
National University of Singapore
Monday, 13. December 2021 - 16:00 to 17:30

Zoom meeting 472 648 284 - https://cesnet.zoom.us/j/472648284 - contact thapen@math.cas.cz to join

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TBA

Damir Dzhafarov
University of Connecticut and Charles University
Monday, 8. November 2021 - 16:00 to 17:30

Zoom meeting 472 648 284 - https://cesnet.zoom.us/j/472648284 - contact thapen@math.cas.cz to join

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TBA

Ilario Bonacina
UPC Barcelona
Monday, 25. October 2021 - 16:00 to 17:30

IM, rear building, ground floor

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A super-polynomial separation between resolution and cut-free sequent calculus

Theodoros Papamakarios
University of Chicago
Monday, 4. October 2021 - 16:00 to 17:30

Zoom meeting 472 648 284 - https://cesnet.zoom.us/j/472648284 - contact thapen@math.cas.cz to join

We show a quadratic separation between resolution and cut-free sequent calculus width. We use this gap to get, first, a super-polynomial separation between resolution and cut-free sequent calculus for refuting CNF formulas, and secondly, a quadratic separation between resolution width and monomial space in polynomial calculus with resolution. Our super-polynomial separation between resolution and cut-free sequent calculus only applies when clauses are seen as disjunctions of unbounded arity; our examples have linear size cut-free sequent calculus proofs writing, in a particular way, their clauses using binary disjunctions. Interestingly, this shows that the complexity of sequent calculus depends on how disjunctions are represented.

LEARN-Uniform Circuit Lower Bounds and Provability in Bounded Arithmetic

Marco Carmosino
Boston University
Monday, 14. June 2021 - 15:45 to 17:15
Zoom meeting 472 648 284 - https://cesnet.zoom.us/j/472648284 - contact thapen@math.cas.cz to join
We investigate randomized LEARN-uniformity, which captures the power of randomness and equivalence queries (EQ) in the construction of Boolean circuits for an explicit problem. This is an intermediate notion between P-uniformity and non-uniformity motivated by connections to learning, complexity, and logic. Building on a number of techniques, we establish the first unconditional lower bounds against LEARN-uniform circuits. For example:

For each k >= 1, there is a language L in NP such that circuits for L of size O(n^k) cannot be learned in deterministic polynomial time with access to n^o(1) EQs.

We employ such results to investigate the (un)provability of non-uniform circuit upper bounds (e.g., Is NP contained in SIZE[n^3]?) in theories of bounded arithmetic. Some questions of this form have been addressed in recent papers of Krajicek-Oliveira (2017), Muller-Bydzovsky (2020), and Bydzovsky-Krajicek-Oliveira (2020) via a mixture of techniques from proof theory, complexity... more

A Diagonalization-Based Approach to Proof Complexity

Iddo Tzameret
Imperial College London
Monday, 7. June 2021 - 15:45 to 17:15
Zoom meeting 472 648 284 - https://cesnet.zoom.us/j/472648284 - contact thapen@math.cas.cz to join
We propose a diagonalization-based approach to several important questions in proof complexity. We illustrate this approach in the context of the algebraic proof system IPS and in the context of propositional proof systems more generally.

We use the approach to give an explicit sequence of CNF formulas phi_n such that VNP \neq VP iff there are no polynomial-size IPS proofs for the formulas phi_n. This provides the first natural equivalence between proof complexity lower bounds and standard algebraic complexity lower bounds. Our proof of this fact uses the implication from IPS lower bounds to algebraic complexity lower bounds due to Grochow and Pitassi together with a diagonalization argument: the formulas phi_n themselves assert the non-existence of short IPS proofs for formulas encoding VNP \neq VP at a different input length. Our result also has meta-mathematical implications: it gives evidence for the difficulty of proving strong lower bounds for IPS within IPS.

For any... more

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