Lean proof assistant ships with verified kernels for safer code checking

Lean v4.35.0 now includes verified kernels to enhance reliability in proof checking. The release introduces con-leche, a Lean-written kernel proven consistent via set theory models, and con-ron, a Rust-translated version verified using Aeneas. Both kernels eliminate implementation bugs in the proof checker without performance loss. Additional kernels like nanoda and lean4lean are available, with lean4lean’s verification expected soon. The update also adds a sandboxed ‘lake check’ command for revalidating developments against multiple kernels, reducing risks from compiler or runtime errors. Future work includes simplifying kernels, improving scalability for large projects, and enabling user-customizable kernel checks. The Lean community faces challenges with growing codebases exceeding 1B lines of code, necessitating binary exports and incremental checking tools.