Course in mathematical analysis - Goursat , Edward (New York Dover, 1959)
v. 1: Derivates and differentials : Definite integrals expansion in series applications to geometry, translated by Earle Raymond Hedrick
v.2: pt . ii . differential equations, translated by Earle Raymond Hedrick and Otton Dunkel
v.3: pt.ii. Integral equations calculus of variations, translated by Howard G. Bergmann