Getting Started with Lean 4: Proofs as Code for Real Developers

tl;dr — Lean 4 is best understood as proof engineering for developers: a language where programs, proofs, and formal specifications live in one workflow. The practical path in is clear: install elan, create a Lake project, add mathlib4, pull the precompiled cache with lake exe cache get, and work inside VS Code + InfoView so you can see goals, hypotheses, errors, and proof state live as you edit. The conceptual shift is equally important: in Lean, proofs are typed programs, and tactics like intro, exact, apply, rw, simp, ext, cases, and induction are the developer’s control surface for building correctness interactively. The upside is stronger precision, structure, and feedback-driven reasoning; the tradeoff is a real learning curve, especially around theorem discovery, library search, and initial toolchain setup.

Lean is an open-source functional programming language and interactive theorem prover (also known as a proof assistant).

• Math as Code: Lean allows you to write mathematical…