GOURSAT, Leçons sur le Problème de Pfaff, 1922

First edition.
Édouard Goursat (1858-1936) was a French mathematician, a member of the Institut, and a professor at the Faculty of Sciences in Paris. He is best known for his work on functions of a complex variable and partial differential equations. This work is a series of lectures on the Pfaff problem, a problem in differential geometry that has applications in theoretical physics.