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Fermat's Last Theorem
historic
Posed by Pierre de Fermat · 1637 · number theory · resolved 1995 · ~1 min read
· difficulty 5/5
diophantine-equations modular-forms
The problem
Theorem: the equation \(x^n\) + \(y^n\) = \(z^n\) has no solutions in positive integers x, y, z when n > 2. Fermat noted in 1637 that he had a marvellous proof; the margin was too narrow to contain it. Proven by Andrew Wiles in 1995 via the modularity of semistable elliptic curves.
History & significance
Written by Fermat in his copy of Diophantus around 1637 with the fatal words "I have discovered a truly marvellous proof of this, which this margin is too narrow to contain." Euler settled n = 3; Dirichlet and Legendre n = 5; Kummer built ideal theory reaching all regular exponents. Sophie Germains partial programme anticipated modern approaches. In September 2026 the proof gained a second kind of certainty: Claude, working largely autonomously over 11 days on the Prove2Me platform, produced the first complete computer-checked formalization — about 13 million lines of Lean, 29,500 intermediate theorems, following the Darmon–Diamond–Taylor exposition and checked by Lean's kernel plus an independent second kernel. No new mathematics; the first end-to-end machine verification of a proof at this scale, building on Mathlib and Buzzard's community FLT project.
Connected problems
References
The resolution (human proof)
Proved by Andrew Wiles — announced June 1993, repaired with Richard Taylor, published 1995. The proof proves the Taniyama–Shimura modularity conjecture for semistable elliptic curves: FLT follows because a counterexample would yield a non-modular semistable curve (Frey's 1985 observation, Ribet's 1986 theorem). Seven years of secret work; the 1993 gap took another eighteen months. The archetypal century-scale human conquest — and the template for how a single mind with the right structures can end a 358-year story.
How to check it: two Annals papers — Wiles (1995) plus Taylor–Wiles on the ring-theoretic lifting step. The Taylor–Wiles method outgrew FLT itself: pushed to full modularity (Breuil–Conrad–Diamond–Taylor 2001), it became the engine room of modern number theory. See the modularity theorem entry here.
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