The arrival of AI has made mathematical exploration incredibly exciting. On one hand, we can now imagine a future where a major unsolved math conjecture—something once considered completely out of reach—is solved by a high school student simply with the help of AI. At the same time, AI gives us a powerful way to expose self-proclaimed "geniuses" who claim to have cracked century-old problems. Just hand them Lean: if their proof doesn't "compile," the illusion collapses instantly. Lean is a modern interactive theorem prover (ITP) and a powerful functional programming language rolled into one. It lets users express mathematical theorems, definitions, and proofs as precise, machine-verifiable code. The Lean kernel then automatically checks the logic for correctness. If the code "compiles"—that is, passes the type checker—the proof is rigorously verified as correct. By turning mathematical proofs into verifiable code, Lean dramatically increases reliability and is accelerating the construction of massive formalized mathematics libraries—with the ambitious goal of formalizing all of contemporary mathematics. More than just a tool, Lean serves as a powerful bridge connecting mathematics, computer science, and AI.