[In the margin of his copy of Diophantus'Arithmetica, Fermat wrote]

To divide a cube into two other cubes, a fourth power or in general any power whatever into two powers of the same denomination above the second is impossible, and I have assuredly found an admirable proof of this, but the margin is too narrow to contain it.

And perhaps, posterity will thank me for having shown it that the ancients did not know everything.

Whenever two unknown magnitudes appear in a final equation, we have a locus, the extremity of one of the unknown magnitudes describing a straight line or a curve.