We construct uniquely satisfiable k-CNF formulas that are hard for the algorithm PPSZ. Firstly, we construct graph-instances on which “weak PPSZ” has savings of at most (2 + ǫ)/k; the saving of an algorithm on an input formula with n variables is the largest γ such that the algorithm succeeds (i.e. finds a satisfying assignment) with probability at least 2. Since PPSZ (both weak and strong) is ...

We prove exponential lower bounds on the running time of many algorithms for Constraint Satisfaction, by giving a simple family of instances on which they always take exponential time. Although similar lower bounds for most of these algorithms have been shown before, we provide a uniform treatment which illustrates a powerful general approach and has stronger impfications for the practice of al...

Sparse hard sets for complexity classes has been a central topic for two decades. The area is motivated by the desire to clarify relationships between completeness/hardness and density of languages and studies the existence of sparse complete/hard sets for various complexity classes under various reducibilities. Very recently, we have seen remarkable progress in this area for low-level complexi...

We define a new heuristic hDS for ASP, and implement it in the (disjunctive) ASP system DLV. The new heuristic improves the evaluation of Σ2 /Π P 2 hard ASP programs while maintaining the benign behaviour of the well-assessed heuristic of DLV on NP problems. We experiment with the new heuristic on QBFs. hDS significantly outperforms the heuristic of DLV on hard 2QBF problems. We compare also th...

Network worms-self-propagating network programs-represent a substantial threat to our network infrastructure. Due to the propagation speed of worms, reactive defenses need to be automatic. It is important to understand where and how these defenses need tu fit in the network so that they cannot he easily evaded. As there are several mechanisms malcode authors can use to bypass existing perimeter...

The processes discussed in this talk were ep → eMp, ep → eγp, and ep → eμμp, all in the deep-inelastic region where Q is large. The factorization theorems that I will discuss provide a sound basis for the phenomenology of these processes, which was discussed extensively at this workshop. They express the amplitudes for the processes in terms of operator matrix elements and perturbatively calcul...