Some Existence Theorems in the Calculus of Variations III. Existence Theorems for Nonregular Problems
E. J. McShane · Transactions of the American Mathematical Society · 1939
E. J. McShane, Some Existence Theorems in the Calculus of Variations III. Existence Theorems for Nonregular Problems, Transactions of the American Mathematical Society, Vol. 45, No. 1 (Jan., 1939), pp. 151-171