1. Lectures on the Calculus of Variations;Bolza,1904
2. Fondamenti di Calcolo delle Variazioni I e II;Tonelli,1921
3. Calculus of Variations and Partial Differential Equations of First Order;Caratheodory,1982
4. Lectures on the Calculus of the Variations;Bliss,1946
5. Variational Analysis;Morse,1973