A group divisible design GDD(v = 3+n+n, 3, 3, λ1, λ2) is an ordered pair (V, B) where V is an (3 + n + n)-set of symbols and B is a collection of 3-subsets (called blocks) of V satisfying the following properties: the (3 + n + n)-set is divided into 3 groups of sizes 3, n and n; each pair of symbols from the same group occurs in exactly λ1 blocks in B; and each pair of symbols from different groups occurs in exactly λ2 blocks in B. Let λ1, λ2 be positive integers. |