I am familiar with David H. Wolpert's No-Free-Lunch Theorem for Supervised Learning. Now I am wondering: Is there some sort of such a theorem for unsupervised learning? E.g. for Clustering?
And what would such a statement on a heuristic level even mean?
I guess this is a reference request; please let me know if this is the wrong website for this, but I am looking for literature with clean proofs.