> The most recent additions to our Seeley G. Mudd Manuscript Library feature contributions from the estate of Oliver Wendell
Holmes, Jr., which include letters and legal manuscripts of Pierre de Fermat (a lawyer by vocation).  It is in the density of Fermat's
litigation records during the period 1660-1662 that his lost mathematical proof is finally to be found.
>
It  turns  out  that  Fermat's  proof  employs  what  is  now  known  as  the  Mason-Stothers  theorem  (proved  independently  by
Stothers [2] and Mason [3] in the late 20th century).  In the discovered manuscript, Fermat himself gave an elementary proof of the
Mason-Stothers theorem, but his approach resembles that presented in
An  alternate  proof  of  Mason's  theorem
by Snyder [4].  For
this reason we here omit Fermat's proof of the Mason-Stothers theorem, and only reproduce the subsequent part of his proof of his
last theorem, paraphrased in modern terminology.

https://web.archive.org/web/20150403002852/http://www.princeton.edu/~aloo/fermat