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It's been known since before Pythagoras that if the lengths of the sides of a right-angled triangle are a, b and c,

with c the longest, then a, b and c satisfy the equation EQN:a^2+b^2=c^2.

[[[>50 This is a simple example _ of a Diophantine equation. ]]]

That equation has many solutions in which a, b and c which are integers. For example:

* a=5, b=12 and c=13

* a=7, b=24 and c=25

* a=8, b=15 and c=17

Fermat made the hypothesis that EQN:a^n+b^n=c^n has no integer solutions when n > 2.

In 1637 he wrote, in his copy of Claude-Gaspar Bachet's translation of the famous Arithmetica of Diophantus,

"I have a truly marvellous proof of this proposition which this margin is too narrow to contain."

(Original Latin: !/ "Cuius rei demonstrationem mirabilem sane detexi. Hanc marginis exiguitas non caperet."

He omitted to write it down anywhere else.

For over 350 years many

British

It is now generally believed that

which the flaw is to use something which at the time was generally thought to be true, but was later

shown to be false. This is, of course, sheer speculation, but it is mildly satisfying.