This is a survey paper on optimization problems via the technique of first and second order tangent cones to a nonempty subset of a Banach space X. Such a technique is also used in the study of the flow invariance of a closed set with respect to a second order differential equation (motion on a given orbit in a force field). Many of the known results in these areas are included here.
"Optimization and Flow Invariance via First and Second Order Tangent Cones." Afr. Diaspora J. Math. (N.S.) 12 (2) 134 - 148, 2011.