“…While the condition is necessary for a point to be a local minimizer of a general d.c. function (see, e.g., [4, Subsection 2.2], [5,Section 5]), its sufficiency is proved only for the case where the second d.c. component is polyhedral, see, e.g., [4]. Necessity of this condition can be considered as a consequence of optimality condition obtained by Demy'anov et al in quasidifferential calculus; see, for instance, [6, Theorem 5.1] and [7, Theorem 3.1].…”