Thanks! So if I read your comment correctly there is nothing inherently wrong with the Comparable interface it's just that Clojure's sorted sets and maps could have used protocols instead. I can see why that would be useful for extending existing types (as you mentioned).

OTOH it’s not often I’ve seen third-party types that I wanted to be comparable but were not. In general I think that if a type does not implement a core interface you have to consider the possibility that the designer chose not to implement it for a reason.