Abstract
A class of propositional formulas, encoding the property that every finite, transitive digraph with no two-cycles must have a source, has been investigated by Krishnamurty and conjectured as hard for resolution. In this note we prove, opposed to that conjecture, that there are proofs of polynomial lengths (or even linear in the lengths of the formulas) of those formulas.
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Stålmarck, G. Short resolution proofs for a sequence of tricky formulas. Acta Informatica 33, 277–280 (1996). https://doi.org/10.1007/s002360050044
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DOI: https://doi.org/10.1007/s002360050044