Improving Depth-First Pn-Search: 1+Epsilon Trick

Various efficient game problem solvers are based on PN-Search. Especially depth-first versions of PN-Search like DF-PN or PDS - contrary to other known techniques - are able to solve really hard problems. However, the performance of DF-PN and PDS decreases drastically when the search space significantly exceeds the available memory. A straightforward enhancement trick to overcome this problem is presented. Experiments on Atari Go and Lines of Action show great practical value of the proposed enhancement.