A multiplier rule is proved for constrained minimization problems defined on a metric spaces. The proof requires a generalization of the values of a derivative in the classical case that the metric space is a normed space. © 2007 Elsevier Inc. All rights reserved.
McAsey, M., & Mou, L. (2008). A multiplier rule on a metric space. Journal of Mathematical Analysis and Applications, 337(2), 1064–1071. https://doi.org/10.1016/j.jmaa.2007.04.027