Non-binary bottom-up constituency parsing without arity actions

# Non-binary bottom-up constituency parsing without arity actions
Source: [https://arxiv.org/abs/2607.10591](https://arxiv.org/abs/2607.10591)
[View PDF](https://arxiv.org/pdf/2607.10591)

> 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\.

## Submission history

From: Jungyeul Park \[[view email](https://arxiv.org/show-email/a8996f80/2607.10591)\] **\[v1\]**Sun, 12 Jul 2026 06:07:29 UTC \(109 KB\)