1. Lectures on the Calculus of Variations;Bliss,1946
2. Vorlesungen über Reelle Funktionen;Carathéodory,1927
3. Theory of Ordinary Differential Equations;Coddington,1955
4. Theory of Functions of Real Variables;Graves,1956
5. Leçons sur le Calcul des Variations;Hadamard,1910