Optimization Theory in Linear Spaces. Part III. Mathematical Programming in Partially Ordered Banach Spaces. K. RITTER — 1970 Mathematische Annalen
Optimization Theory in Linear Spaces. Part II. On Systems of Linear Operator Inequalities in Partially Ordered Normed Linear Spaces. K. RITTER — 1969 Mathematische Annalen
On the Rate of Superlinear Convergence of a Class of Variable Metric Methods. K. Ritter — 1980 Numerische Mathematik