Multidirectional Mean Value Inequalities in Quasidifferential Calculus

In the current paper, a Clarke–Ledyaev type mean value inequality is proved for semicontinuous functions defined in a Banach space that are quasidifferentiable in the sense of Demyanov–Rubinov. A stronger variant valid under compactness assumption in separable spaces and extensions for functions with semicontinuous Dini derivatives in locally uniformly convex Banach spaces and with merely bounded Dini derivatives are then established. Subsequently, applications of these mean value inequalities to solvability of nonsmooth parametric equations and to the estimation of local and global Hoffman error bound for inequalities are investigated via a decrease principle.