@inproceedings{NeurIPS'23:universal,
    author = {Yu-Hu Yan and
                    Peng Zhao and
                    Zhi-Hua Zhou},
    title = {Universal Online Learning with Gradual Variations: A Multi-layer Online Ensemble Approach},
    booktitle = {Advances in Neural Information Processing Systems 36 (NeurIPS)},
    pages = {to appear},
    year = {2023}
}