We study online learnability of a wide class of problems, extending the results of (Rakhlin, Sridharan, Tewari, 2010) to general notions of performance measure well beyond external regret. Our framework simultaneously captures such well-known notions as internal and general Phi-regret, learning with non-additive global cost functions, Blackwell's approachability, calibration of forecasters, adaptive regret, and more. We show that learnability in all these situations is due to control of the same three quantities: a martingale convergence term, a term describing the ability to perform well if future is known, and a generalization of sequential Rademacher complexity, studied in (Rakhlin, Sridharan, Tewari, 2010). Since we directly study complexity of the problem instead of focusing on efficient algorithms, we are able to improve and extend many known results which have been previously derived via an algorithmic construction.

本研究探讨了一类广泛问题的在线可学性，并将其扩展到远超过外部遗憾的性能评估简单规范。我们的框架同时捕捉了其他著名规范，例如内部和一般Phi规范、学习使用非加性全局成本函数、Blackwell的可挑战性、预测者的校准、自适应遗憾等。我们展示了在所有这些情况下的可学习性归因于控制相同的三个量：马田哥小定理收敛项、如果已知未来则能够表现良好的能力描述项、以及顺序Rademacher复杂性的概括，该复杂性在(Rakhlin, Sridharan, Tewari, 2010)中得到研究。由于我们直接研究问题的复杂性，而不是专注于高效算法的开发，因此我们能够改进和扩展许多已知结果，这些结果之前是通过算法构造推导出来的。

在线学习：超越遗憾