[I locally answered this question last time already, but it looks like my mail never reached the mailing list due to a local misconfiguration at the time] Op 20-09-12 01:49, Ricardo schreef: Use a difficulty comparator if you can: it's the easy variant. A difficulty weight factory is needed only if you need the entire Solution (not just the entity) to calculate the difficulty of a given entity. In the examples, look for *DifficultyComparator and *DifficultyWeightFactory.