{"ID":6536136,"CreatedAt":"2026-07-14T01:21:01.169441415Z","UpdatedAt":"2026-07-15T03:28:55.185153975Z","DeletedAt":null,"paper_url":"https://arxiv.org/abs/2607.10591","arxiv_id":"2607.10591","title":"Non-binary bottom-up constituency parsing without arity actions","abstract":"Non-binary bottom-up constituency parsing is usually taken to require arity actions: reductions such as \\(\\textsc{Reduce-}X\\#k\\) specify both the mother label and the number of children to be composed. We show that this arity parameter is not a necessary transition primitive. Our parser introduces constituent labels separately and recovers reduction spans from delimiter-bounded stack configurations. In a well-formed reduction configuration, arity is uniquely determined by the active delimiter and the label marker, making it a derived property of parser state rather than an action label. This factorization removes label--arity-specific reduce actions while preserving direct construction of original non-binary trees. Experiments on PTB and CTB show that the delimiter-guided parser remains competitive with an arity-specific bottom-up baseline under the same implementation framework, with substantially smaller action inventories. Analyses further show that its predicted arity profile remains close to the gold treebanks and that high-arity constituents do not collapse when arity actions are removed.","short_abstract":"Non-binary bottom-up constituency parsing is usually taken to require arity actions: reductions such as \\(\\textsc{Reduce-}X\\#k\\) specify both the mother label and the number of children to be composed. We show that this arity parameter is not a necessary transition primitive. Our parser introduces constituent labels se...","url_abs":"https://arxiv.org/abs/2607.10591","url_pdf":"https://arxiv.org/pdf/2607.10591v1","authors":"[\"Jungyeul Park\",\"Eunkyul Leah Jo\",\"Zihao Huang\"]","published":"2026-07-12T06:07:29Z","proceeding":"cs.CL","tasks":"[\"cs.CL\"]","methods":"[]","has_code":false}