Pierre de Fermat (August 17, 1601 or 1607 - January 12, 1665) was a French lawyer at the Parlement of Toulouse, France, and an amateur mathematician who is given credit for early developments that led to infinitesimal calculus. He is remembered for his discovery of an original method of finding the greatest and the smallest ordinates of curved lines, which is analogous to that of the then unknown differential calculus, and his research into number theory. He made notable contributions to analytic geometry, probability, and optics. He is best known for Fermat's Last Theorem, which he described in a note at the margin of a copy of Diophantus' Arithmetica. Fermat was the first person known to have evaluated the integral of general power functions. His formula was helpful to Newton, and then Leibniz, when they independently developed the fundamental theorem of calculus. Together with Ren矇 Descartes, Fermat was one of the two leading mathematicians of the first half of the 17th century.