# Lean adds verified proof checkers and sandboxed rechecking

_Published Sunday, October 18, 2026 at 2:07 AM EDT · Products · Latest · Tier 2 — Notable_

Lean v4.35.0 adds a command that rechecks mathematical proofs inside a sandbox, and Lean now ships four additional proof-checking kernels, according to the project's announcement. The command's paranoid mode runs all four plus an official kernel variant that turns memory corruption into a checked abort.

One new kernel, con-leche, has a formal consistency proof: environments it accepts have a model in set theory. A Rust translation, con-ron, has been verified to follow its checking algorithm, providing another route to catch compiler or runtime faults.

The consistency proof assumes the underlying set theory is consistent. The current external-checking approach also cannot scale to the largest developments described by the project.

## Sources

- [leodemoura.github.io](https://leodemoura.github.io/blog/2026-10-15-lean-now-ships-with-verified-kernels/)

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Canonical: https://techandbusiness.org/newswire/VcPFXYhcxMRWBUMmOzPQFL
Published: 2026-10-18T06:07:13.191Z
Story chronology: 2026-10-16T06:16:13.000Z
Retrieved: 2026-10-18T08:36:30.331Z
Publisher: Tech & Business (techandbusiness.org)