>As I indicate on page 1, Chapter 1, of my manuscript on
>the evolution of reciprocity laws from Euler to Artin
> ( http://www.rzuser.uni-heidelberg.de/~hb3/rec.html ),
>according to J. Hofmann,
>"Uber die zahlentheoretischen Methoden Fermats und
> Eulers, ihre Zusammenh"ange und ihre Bedeutung},
>Archive for History of Exact Sciences 1 (1960/62), 122--159,
>Fermat's 2-squares theorem first appeared in a book of Simon Stevin.
>As others have already remarked, apparently nobody doubts that
>Fermat was the first who could prove this, and that the first
>published proof was Euler's.
>
>bye,
>
> franz
>
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This book of Simon Stevin was "L'Arithmétique de Simon Stevin de Bruges, revue, corrigee & augmentee de plusieurs traictez et
annotations par Albert Girard Samielois Mathematicien", published in 1625 ( "Samielois" means : born in Saint-Mihiel). It was a French
translation from Flamish, with some additions by Girard. I wrote an article in "Pour la Science", April 1986, on this theorem ("Le plus
beau théorème de Fermat" ) in which one can see the page of title of this book and the copy of the statement of this theorem by Girard :
"Determinaison d'un nombre qui se peut diviser en deux quarrez entiers".
Best regards to Mr Lemmermeyer, and I hope to read his book soon.
RC