In terms of the use case, I’d like to find an element in a set. If the element is there, I’d like to get it back (not just the fact that it exists). If it is not in the set, I’d like to get the next higher and the next lower one (according to the sort order). This is almost exactly what splitLookup does, however, splitLookup gives me both the trees, whereas I only would need the elements of the set.