1. “Lectures on the Calculus of Variations.”;Bolza,1904
2. The minimum of a definite integral with respect to unilateral variation;Mancil,1933
3. Problem of Lagrange with differential inequalities;Valentine,1933
4. Singularities in a variational problem with an inequality;Garfinkel;Pacific J. Math.,1966
5. “Lectures on the Calculus of Variations.”;Bliss,1946