Short proofs may be spacious: An optimal separation of space and length in resolution

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A number of works have looked at the relationship between length and space of resolution proofs. A notorious question has been whether the existence of a short proof implies the existence of a proof that can be verified using limited space. In this paper we resolve the question by answering it negatively in the strongest possible way. We show that there are families of 6-CNF formulas of size n, for arbitrarily large n, that have resolution proofs of length O(n) but for which any proof requires space Ω(n/log n). This is the strongest asymptotic separation possible since any proof of length O(n) can always be transformed into a proof in space O(n/log n). Our result follows by reducing the space complexity of so called pebbling formulas over a directed acyclic graph to the black-white pebbling price of the graph. The proof is somewhat simpler than previous results (in particular, those reported in [Nordström 2006, Nordström and Håstad 2008]) as it uses a slightly different flavor of pebbling formulas which allows for a rather straightforward reduction of proof space to standard black-white pebbling price.

Original languageEnglish
Title of host publicationProceedings of the 49th Annual IEEE Symposium on Foundations of Computer Science, FOCS 2008
Number of pages10
Publication date2008
Pages709-718
Article number4691003
ISBN (Print)9780769534367
DOIs
Publication statusPublished - 2008
Event49th Annual IEEE Symposium on Foundations of Computer Science, FOCS 2008 - Philadelphia, PA, United States
Duration: 25 Oct 200828 Oct 2008

Conference

Conference49th Annual IEEE Symposium on Foundations of Computer Science, FOCS 2008
LandUnited States
ByPhiladelphia, PA
Periode25/10/200828/10/2008
SeriesProceedings - Annual IEEE Symposium on Foundations of Computer Science, FOCS
ISSN0272-5428

ID: 251871095