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Garmelon merged 1 commit into from
Sep 24, 2026
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doc: add release notes for v4.34.1 #951

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3 changes: 3 additions & 0 deletions Manual/Releases.lean
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,7 @@ Author: Joachim Breitner
import VersoManual

import Manual.Releases.«v4_35_0»
import Manual.Releases.«v4_34_1»
import Manual.Releases.«v4_34_0»
import Manual.Releases.«v4_33_1»
import Manual.Releases.«v4_33_0»
Expand Down Expand Up @@ -71,6 +72,8 @@ the differences with the previous version and upgrade your projects.

{include 0 Manual.Releases.«v4_35_0»}

{include 0 Manual.Releases.«v4_34_1»}

{include 0 Manual.Releases.«v4_34_0»}

{include 0 Manual.Releases.«v4_33_1»}
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47 changes: 47 additions & 0 deletions Manual/Releases/v4_34_1.lean
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@@ -0,0 +1,47 @@
/-
Copyright (c) 2026 Lean FRO LLC. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Author: Joscha Mennicken
-/

import VersoManual
import Manual.Meta
import Manual.Meta.Markdown

open Manual
open Verso.Genre
open Verso.Genre.Manual
open Verso.Genre.Manual.InlineLean

#doc (Manual) "Lean 4.34.1 (2026-09-24)" =>
%%%
tag := "release-v4.34.1"
file := "v4.34.1"
%%%

This patch release contains multiple runtime fixes,
and we encourage all users of v4.34.0 or earlier to upgrade to it.

For this release, 3 changes landed.
In addition to the 0 feature additions
and 3 fixes listed below,
there were 0 refactoring changes,
0 documentation improvements,
0 performance improvements,
0 improvements to the test suite,
and 0 other changes.

# Compiler

```markdown

- [#15289](https://github.com/leanprover/lean4/pull/15289)
makes maximal sharing, including the kernel's sharing of every theorem it checks, panic when a shared subterm gains more than `INT_MAX` references, instead of eventually freeing the subterm while it is still referenced. On inputs north of 100GB, the possibility of triggering undefined behavior this way, which could be extended into a proof of False, could be excluded. Other kernels such as nanoda or con-leche not based on the Lean runtime or not making use of this specific function were not affected.

- [#15288](https://github.com/leanprover/lean4/pull/15288)
fixes potential undefined behavior when an object with a huge number of incoming references is shared between threads. The official kernel does not use multithreading in its default configuration (as used by comparator and `lake check/compare`), but other Lean-based checkers such as con-leche might be affected.

- [#15241](https://github.com/leanprover/lean4/pull/15241)
prevents deletion cascades from releasing objects whose reference count has been frozen after over- or underflow. Like #14838, on machines with at least 18GB of free RAM, it could potentially be used to trigger use-after-free in the official kernel, which could be extended into a proof of False. Other kernels such as nanoda or con-ron not based on the Lean runtime were not affected.

```
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