Let G be a group of group order h and D be a set of k elements of G. If the set of differences d_i - d_j contains every nonzero element of G exactly λ times, then D is a (h, k, λ)-difference set in G of order n = k - λ. If λ = 1, the difference set is called planar. The quadratic residues in the finite field G F(11) form a difference set. If there is a difference set of size k in a group G, then 2(k 2) must be a multiple of left bracketing bar G right bracketing bar - 1, where (k 2) is a binomial coefficient. Gordon maintains an index of known difference sets.

Bruck-Ryser-Chowla theorem | first multiplier theorem | prime power conjecture | set difference