Beyond the Erdős-Ko-Rado theorem
Journal of Combinatorial Theory Series A
The complete nontrivial-intersection theorem for systems of finite sets
Journal of Combinatorial Theory Series A
An Erdős-Ko-Rado theorem for direct products
European Journal of Combinatorics
Sperner theory
The complete intersection theorem for systems of finite sets
European Journal of Combinatorics
Regular Article: The Diametric Theorem in Hamming Spaces驴Optimal Anticodes
Advances in Applied Mathematics
The intersection theorem for direct products
European Journal of Combinatorics
Forbidden (0,1)-vectors in Hyperplanes of $$\mathbb{R}^{n}$$: The unrestricted case
Designs, Codes and Cryptography
Bibliography of publications by Rudolf Ahlswede
Information Theory, Combinatorics, and Search Theory
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In Ahlswede et al. [Discrete Math. 273(1-3) (2003) 9-21] we posed a series of extremal (set system) problems under dimension constraints. In the present paper, we study one of them: the intersection problem. The geometrical formulation of our problem is as follows. Given integers 0 ≤ t, k ≤ n determine or estimate the maximum number of (0, 1)-vectors in a k-dimensional subspace of the Euclidean n-space Rn, such that the inner product ("intersection") of any two is at least t. Also we are interested in the restricted (or the uniform) case of the problem; namely, the problem considered for the (0, 1)-vectors of the same weight ω.The paper consists of two parts, which concern similar questions but are essentially independent with respect to the methods used.In Part I, we consider the unrestricted case of the problem. Surprisingly, in this case the problem can be reduced to a weighted version of the intersection problem for systems of finite sets. A general conjecture for this problem is proved for the cases mentioned in Ahlswede et al. [Discrete Math. 273(1-3) (2003) 9-21]. We also consider a diametric problem under dimension constraint.In Part II, we study the restricted case and solve the problem for t = 1 and k t ≤ ω and k large.