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Logic seminar

usually takes place each Monday at 16:00 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.

Towards P != NP from Extended Frege lower bounds

Ján Pich
University of Oxford
Monday, 12. December 2022 - 16:00 to 17:30
Large lecture room at Zitna and online at https://cesnet.zoom.us/j/472648284 - contact thapen@math.cas.cz before the meeting to join online
We prove that if conditions I-II (below) hold and there is a sequence of Boolean functions $f_n$ hard to approximate by p-size circuits such that p-size circuit lower bounds for $f_n$ do not have p-size proofs in Extended Frege system EF, then $P \ne NP$.

I. $S^1_2$ proves that there is a function $g\in E$ hard to approximate by subexponential-size circuits.

II. (Learning from the non-existence of OWFs.) $S^1_2$ proves that a p-time reduction transforms circuits breaking one-way functions to p-size circuits learning p-size circuits over the uniform distribution, with membership queries.

Here, $S^1_2$ is Buss's theory of bounded arithmetic formalizing p-time reasoning.

Further, we show that any of the following assumptions implies that $P \ne NP$, if EF is not p-bounded:

1. (Feasible anticheckers.) $S^1_2$ proves that a p-time function generates anticheckers for SAT.

2. (Witnessing $NP\not\subseteq P/poly$.) $S^1_2$ proves that a p-time... more

On the parameterized complexity of Delta-0 truth

Moritz Müller
University of Passau
Monday, 21. November 2022 - 16:00 to 17:30
Online - https://cesnet.zoom.us/j/472648284 - contact thapen@math.cas.cz before the meeting to join
We consider the problem, given a Δ0 formula φ(x) and a natural number n in unary, whether φ(n) is true. We are interested in instances of the problem where n is much bigger than φ. More precisely, we consider the parameterized problem with parameter |φ|. We show unconditionally that this problem does not belong to the parameterized version of AC0. We also show that certain natural upper bounds on the parameterized complexity of the problem imply separations of classical complexity classes. These results are obtained by an analysis of a parameterized halting problem. A related problem concerns the provability of the MRDP theorem in bounded arithmetic.

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