It is written in terms of std::next_permutation. I needed to iterate over all possible combinations of EG-clusters being matched to PF clusters and minimize a residual. This allows me to do it with reasonable timing and significantly less debugging. When we make the final switch to PF SuperClusters, this code can go away (i.e. it'll be gone in the March release). It is moved now anyway to the src directory, no one should use it from there.