Hard choices, no easy solutions

Using the No-Search Easy-Hard Technique for Downward Collapse

Σ k Π k DIFFm(Σ p k ) coDIFFm(Σ p k ) P Σ p k m-tt P Σ p k m+1-tt BH(Σ k ) Supported in part by grants NSF-CCR-9322513, NSF-INT-9513368/DAAD-315-PRO-fo-ab, and NSF-INT9815095/DAAD-315-PPP-gü-ab, and a NATO Postdoctoral Science Fellowship from the DAAD’s “Gemeinsames Hochschulsonderprogramm III von Bund und Ländern” program. This report combines and extends each of technical reports corr-cs.CC/9...

Easy Problems are Sometimes Hard

We present a detailed experimental investigation of the easy-hard-easy phase transition for randomly generated instances of satisfiability problems. Problems in the hard part of the phase transition have been extensively used for benchmarking satisfiability algorithms. This study demonstrates that problem classes and regions of the phase transition previously thought to be easy can sometimes be...

Easy and Hard Conformant Planning

Even under polynomial restrictions on plan length, conformant planning remains a very hard computational problem as plan verification itself can take exponential time. This heavy price cannot be avoided in general although in many cases conformant plans are verifiable efficiently by means of simple forms of disjunctive inference. We report an efficient but incomplete planner capable of solving ...

Distinguishing Easy and Hard Instances

Easy solutions for a hard problem? The computational complexity of reciprocals with quantificational antecedents

The PTIME-Cognition Hypothesis states that cognitive capacities are limited to those functions that are computationally tractable (Frixione 2001). We applied this hypothesis to semantic processing and investigated whether computational complexity affects interpretation preferences of reciprocal sentences with quantificational antecedents, that is sentences of the form Q dots are (directly) conn...