Doug Ward, “Directional Derivative Calculus and Optimality Conditions in Nonsmooth Mathematical Programming”, Journal of Information and Optimization Sciences, 10:1 (1989), 81
N Hadjisavvas, D Kravvaritis, G Pantelidis, I Polyrakis, “Nonlinear monotone operators with values in L(X, Y)”, Journal of Mathematical Analysis and Applications, 140:1 (1989), 83
Doug Ward, “Which subgradients have sum formulas?”, Nonlinear Analysis: Theory, Methods & Applications, 12:11 (1988), 1231
Doug Ward, “Convex subcones of the contingent cone in nonsmooth calculus and optimization”, Trans. Amer. Math. Soc., 302:2 (1987), 661
А. В. Бухвалов, “Приложения методов теории порядково ограниченных операторов к теории операторов в пространствах $L^p$”, УМН, 38:6(234) (1983), 37–83 ; A. V. Bukhvalov, “Application of methods of the theory of order-bounded operators to the theory of operators in $L^p$-spaces”, Russian Math. Surveys, 38:6 (1983), 43–98