The statement that, for all integers n>2, the equation xⁿ + yⁿ = zⁿ has no solution in positive integers. Fermat famously noted in a copy of Diophantus’ Arithmetica that he had a proof ‘too large fit in the margin’. Much research was done over centuries until a proof was completed in 1995 by Andrew Wiles. See Pythagorean triple, modularity theorem.