Recognition: unknown
LeanSearch v2: Global Premise Retrieval for Lean 4 Theorem Proving
Pith reviewed 2026-05-14 18:28 UTC · model grok-4.3
The pith
LeanSearch v2 recovers full premise groups for Lean 4 theorems and raises proof success from 4% to 20% in controlled tests
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
LeanSearch v2 is a two-mode retrieval system for global premise retrieval in Lean 4. Standard mode applies an embedding-reranker pipeline to a hierarchy-informalized Mathlib corpus and reaches state-of-the-art single-query retrieval. Reasoning mode builds iterative sketch-retrieve-reflect cycles on that substrate to recover the full premise sets required by theorems. On a 69-query benchmark of research-level Mathlib theorems, reasoning mode recovers 46.1% of ground-truth premise groups within the top 10 candidates. In a controlled downstream evaluation with a fixed prover loop, replacing other retrievers with LeanSearch v2 yields 20% proof success compared with 16% for the next-best system.
What carries the argument
Reasoning mode's iterative sketch-retrieve-reflect cycles built on an embedding-reranker pipeline over a hierarchy-informalized Mathlib corpus
If this is right
- Higher-quality global premise retrieval directly increases automated proof success rates inside a fixed Lean 4 prover loop.
- The base retrieval pipeline works without domain-specific fine-tuning yet still outperforms prior systems on single-query and group-recovery tasks.
- Measured recovery of ground-truth premise groups correlates with actual downstream proof-generation performance.
- Open-sourced code, data, and benchmarks make the system reproducible and extensible for further Lean 4 work.
Where Pith is reading between the lines
- Extending the iterative cycles to handle larger or more interdependent premise sets could shrink the search space in interactive theorem proving for advanced mathematics.
- Pairing the retriever with language-model tactic generators may produce stronger combined proof automation pipelines.
- The global-retrieval approach could transfer to other formal libraries and interactive theorem provers that rely on large lemma collections.
Load-bearing premise
The 69-query benchmark and the fixed prover loop are representative of typical research-level Lean 4 usage.
What would settle it
Re-running the evaluation on a larger set of theorems drawn from recent Mathlib contributions or with a different prover configuration that relies less on premise selection would show whether the measured gains hold.
Figures
read the original abstract
Proving theorems in Lean 4 often requires identifying a scattered set of library lemmas whose joint use enables a concise proof -- a task we call global premise retrieval. Existing tools address adjacent problems: semantic search engines find individual declarations matching a query, while premise-selection systems predict useful lemmas one tactic step at a time. Neither recovers the full premise set an entire theorem requires. We present LeanSearch v2, a two-mode retrieval system for this task. Its standard mode applies a hierarchy-informalized Mathlib corpus with an embedding-reranker pipeline, achieving state-of-the-art single-query retrieval without domain-specific fine-tuning (nDCG@10 of 0.62 vs. 0.53 for the next-best system). Its reasoning mode builds on standard mode as its retrieval substrate, targeting global premise retrieval through iterative sketch-retrieve-reflect cycles. On a 69-query benchmark of research-level Mathlib theorems, reasoning mode recovers 46.1% of ground-truth premise groups within 10 retrieved candidates, outperforming strong reasoning retrieval systems (38.0%) and premise-selection baselines (9.3%) on the same benchmark. In a controlled downstream evaluation with a fixed prover loop, replacing alternative retrievers with LeanSearch v2 yields the highest proof success (20% vs. 16% for the next-best system and 4% without retrieval), confirming that retrieval quality propagates to proof generation. We have open-sourced all code, data, and benchmarks. Code and data: https://github.com/frenzymath/LeanSearch-v2 . The standard mode is publicly available with API access at https://leansearch.net/ .
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper introduces LeanSearch v2, a two-mode retrieval system for global premise retrieval in Lean 4 theorem proving. Standard mode uses an embedding-reranker pipeline on a hierarchy-informalized Mathlib corpus to achieve nDCG@10 of 0.62. Reasoning mode adds iterative sketch-retrieve-reflect cycles on top of standard mode, recovering 46.1% of ground-truth premise groups within top-10 candidates on a 69-query benchmark of research-level Mathlib theorems (outperforming 38.0% for strong reasoning systems and 9.3% for premise-selection baselines) and yielding 20% proof success in a fixed downstream prover loop (vs. 16% next-best and 4% without retrieval). All code, data, and benchmarks are open-sourced.
Significance. If the reported empirical gains hold under scrutiny, the work addresses a genuine gap between single-lemma semantic search and per-tactic premise selection by targeting the full scattered premise sets needed for concise proofs. The downstream propagation from retrieval quality to proof success rate is a concrete strength, and the public release of code, data, and the 69-query benchmark supports reproducibility and follow-on work in the Lean community.
major comments (2)
- [Experimental evaluation (benchmark and downstream sections)] The 69-query benchmark and fixed prover loop are load-bearing for the headline claims (46.1% group recovery and 20% proof success). The manuscript provides no description of query selection criteria, no variance estimates across runs, and no statistical significance tests comparing against the 38.0% and 16% baselines; without these, it is impossible to assess whether the measured gaps reflect typical Lean 4 usage or are artifacts of the chosen theorems and prover configuration.
- [Reasoning mode description and results] The reasoning mode's iterative sketch-retrieve-reflect procedure is presented as the key innovation for global retrieval, yet the paper does not report an ablation isolating the contribution of the reflect step versus simply running standard mode multiple times; this leaves open whether the 46.1% figure is driven by the new cycle or by repeated application of the already-strong standard-mode retriever.
minor comments (2)
- [Abstract and §3] The term 'hierarchy-informalized Mathlib corpus' appears in the abstract and method without an explicit definition or pointer to the preprocessing section; adding one sentence of clarification would aid readers unfamiliar with the corpus construction.
- [Results tables] Tables reporting nDCG@10, recall@10, and proof success should include the number of runs or standard deviations if any stochasticity is present in retrieval or proving.
Simulated Author's Rebuttal
We thank the referee for the positive summary, the recognition of the work's significance, and the recommendation for minor revision. We address the two major comments point by point below, indicating the revisions we will make.
read point-by-point responses
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Referee: [Experimental evaluation (benchmark and downstream sections)] The 69-query benchmark and fixed prover loop are load-bearing for the headline claims (46.1% group recovery and 20% proof success). The manuscript provides no description of query selection criteria, no variance estimates across runs, and no statistical significance tests comparing against the 38.0% and 16% baselines; without these, it is impossible to assess whether the measured gaps reflect typical Lean 4 usage or are artifacts of the chosen theorems and prover configuration.
Authors: We agree that the benchmark details require expansion. In the revised manuscript we will add an explicit subsection describing the query selection criteria used to construct the 69-query set of research-level Mathlib theorems. The retrieval and reranking pipelines are deterministic given the fixed corpus, embedding model, and reranker, so variance across runs is exactly zero and does not need to be estimated. The downstream prover loop is likewise run under a fixed, deterministic configuration; we will add a clarifying sentence to this effect. We acknowledge the absence of statistical significance tests. With a benchmark of this size we will instead add a short discussion of the practical magnitude of the observed gains (e.g., lifting proof success from 4 % to 20 %) and note that formal hypothesis testing would have limited power; we do not plan to introduce new multi-seed experiments at this stage. revision: partial
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Referee: [Reasoning mode description and results] The reasoning mode's iterative sketch-retrieve-reflect procedure is presented as the key innovation for global retrieval, yet the paper does not report an ablation isolating the contribution of the reflect step versus simply running standard mode multiple times; this leaves open whether the 46.1% figure is driven by the new cycle or by repeated application of the already-strong standard-mode retriever.
Authors: We accept this criticism. The reflect step is intended to enable dynamic refinement of the search sketch using information from prior retrievals, which is distinct from simply repeating the standard-mode pipeline. To isolate its contribution we will add a new ablation in the revised results section that directly compares (i) the full sketch-retrieve-reflect cycle against (ii) an equal number of iterations of the standard mode alone (without the reflect component). The ablation will be reported alongside the existing 46.1 % figure so that readers can judge the incremental value of the reflect mechanism. revision: yes
Circularity Check
No circularity: empirical benchmark results are direct measurements
full rationale
The paper reports retrieval metrics (nDCG@10, group recovery rates) and downstream proof success rates on a held-out 69-query Mathlib benchmark and a fixed prover loop. These are measured outcomes from running the described embedding-reranker pipeline and iterative sketch-retrieve-reflect cycles; they do not reduce by any equation or self-citation to quantities fitted inside the same run. No uniqueness theorem, ansatz, or self-definitional step is invoked to justify the central claims. The evaluation is self-contained against external baselines and open-sourced code/data.
Axiom & Free-Parameter Ledger
axioms (1)
- domain assumption Mathlib declarations and their informalizations form a representative corpus for research-level Lean 4 theorems
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12 A Benchmark Curation In this section, we present the curation methodology, key characteristics, and illustrative examples of our benchmark to provide readers with a clearer understanding of both the benchmark and the experimental results. We introduce two benchmarks:MathlibQRfor the classical formal theorem searching task, andMathlibMPRfor global premi...
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Table 5: Mean rank conditioned on the system’s randomized label position
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21 Table 10:MathlibQR by difficulty.Half the queries are Easy, half are Hard
Throughout the following tables we abbreviate column headers asLE= LeanEx- plore,LF= LeanFinder,LSv2(r)= LeanSearch v2 retriever-only, andLSv2(rr)= LeanSearch v2 with reranking. 21 Table 10:MathlibQR by difficulty.Half the queries are Easy, half are Hard. nDCG@10Recall@10 Difficulty LE LF LSv2(r) LSv2(rr) LE LF LSv2(r) LSv2(rr) Easy 0.410 0.568 0.5330.666...
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Best per column inbold. Covered (main only) Covered (main∨alt-all) System 5 10 20 30 50 5 10 20 30 50 Reasoning retrieval (informal+formal query) INF-X-Retriever 14.5 17.4 18.8 21.7 21.7 15.9 18.8 21.7 24.6 24.6 +query rewriter 10.1 10.1 14.5 15.9 23.2 10.1 10.1 17.4 17.4 24.6 ReasonIR 15.9 17.4 18.8 18.8 26.1 17.4 18.8 20.3 21.7 30.4 DIVER (full pipeline...
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Table 16:Prover-backbone ablation on FATE-H.Each cell is the count of solved problems out of 100(percentages in parentheses). The Sonnet column reproduces the L0 / L1 / reasoning-mode rows of Table 3; the Kimi column re-runs the same loops with Kimi K2 Instruct in the prover role only. Retrieval mode (prover input) Sonnet prover Kimi prover No retrieval 4...
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discussion (0)
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