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# Open Problem: Is There an Online Learning Algorithm That Learns Whenever Online Learning Is Possible?

*Proceedings of Thirty Fourth Conference on Learning Theory*, PMLR 134:4642-4646, 2021.

#### Abstract

The open problem asks whether there exists an online learning algorithm for binary classification that guarantees, for all target concepts, to make a sublinear number of mistakes, under only the assumption that the (possibly random) sequence of points X allows that such a learning algorithm can exist for that sequence. As a secondary problem, it also asks whether a specific concise condition completely determines whether a given (possibly random) sequence of points X admits the existence of online learning algorithms guaranteeing a sublinear number of mistakes for all target concepts.