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Electronic Colloquium on Computational Complexity

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All reports by Author Joerg Flum:

TR13-065 | 21st April 2013
Yijia Chen, Joerg Flum

On Limitations of the Ehrenfeucht-Fraisse-method in Descriptive Complexity

Ehrenfeucht-Fraisse games and their generalizations have been quite successful in finite model theory and yield various inexpressibility results. However, for key problems such as P $\ne$ NP or NP $\ne$ coNP no progress has been achieved using the games. We show that for these problems it is already hard to ... more >>>

TR12-018 | 24th February 2012
Joerg Flum, Moritz Müller

Some definitorial suggestions for parameterized proof complexity

We introduce a (new) notion of parameterized proof system. For parameterized versions of standard proof systems such as Extended Frege and Substitution Frege we compare their complexity with respect to parameterized simulations.

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TR11-085 | 14th May 2011
Yijia Chen, Joerg Flum, Moritz Müller

Hard instances of algorithms and proof systems

Assuming that the class TAUT of tautologies of propositional logic has no almost optimal algorithm, we show that every algorithm $\mathbb A$ deciding TAUT has a polynomial time computable sequence witnessing that $\mathbb A$ is not almost optimal. The result extends to every $\Pi_t^p$-complete problem with $t\ge 1$; however, we ... more >>>

TR11-020 | 20th December 2010
Yijia Chen, Joerg Flum

Listings and logics

There are standard logics DTC, TC, and LFP capturing the complexity classes L, NL, and P on ordered structures, respectively. In [Chen and Flum, 2010] we have shown that ${\rm LFP}_{\rm inv}$, the ``order-invariant least fixed-point logic LFP,'' captures P (on all finite structures) if and only if there is ... more >>>

TR10-008 | 13th January 2010
Yijia Chen, Joerg Flum

On optimal proof systems and logics for PTIME

Revisions: 1

We prove that TAUT has a $p$-optimal proof system if and only if $L_\le$, a logic introduced in [Gurevich, 88], is a P-bounded logic for P. Furthermore, using the method developed in [Chen and Flum, 10], we show that TAUT has no \emph{effective} $p$-optimal proof system under some reasonable complexity-theoretic ... more >>>

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