Packing radius, covering radius, and dual distance

Tietaivainen (1991) derived an upper bound on the covering radius of codes as a function of the dual distance. This was generalized to the minimum distance, and to Q-polynomial association schemes by Levenshtein and Fazekas. Both proofs use a linear programming approach. In particular, Levenshtein and Fazekas (1990) use linear programming bounds for codes and designs. In this article, proofs relying solely on the orthogonality relations of Krawtchouk (1929), Lloyd, and, more generally, Krawtchouk-adjacent orthogonal polynomials are derived. As a by-product upper bounds on the minimum distance of formally self-dual binary codes are derived