Contents Introduction § 1. Definition of d-convex sets and their simplest properties § 2. Properties of the unit ball § 3. Separability of d-convex sets § 4. Definition of H-convex sets and their simplest properties § 5. Support properties of H-convex sets § 6. Helly's theorem for H-convex sets § 7. A theorem of Szökefalvi-Nagy and its generalization § 8. Applications of Helly's theorem § 9. The Helly dimension of a normed space References
