Hierarchical Indexing for Retrieval-Augmented Opinion Summarization Tom Hosking author Hao Tang author Mirella Lapata author 2024 text journal article Transactions of the Association for Computational Linguistics continuing MIT Press Cambridge, MA periodical academic journal hosking-etal-2024-hierarchical 10.1162/tacl_a_00703 https://aclanthology.org/2024.tacl-1.84/ 2024 12 1533 1555