On the Complexity of Minimum Riesz s-Energy Subset Selection in Euclidean and Ultrametric Spaces Michael T. M. Emmerich, Ksenia Pereverdieva, André Deutz arxiv.org/abs/2605.04715 [𝚌𝚜.𝙲𝙶 𝚌𝚜.𝙲𝙲 𝚖𝚊𝚝𝚑.𝙾𝙲]