Covering t-sets with (t+2)-sets

New upper bounds for C(v, k, t), the minimum number of ii-subsets (blocks) out of a v-set such that each t-subset is contained in at least one block, are obtained by constructing corresponding covering designs with prescribed automorphisms. Computer search with a stochastic heuristic, tabu search, i s used to find the covering designs. The new covering designs are listed an d a table of upper bounds on C(v,t + 2,t) for v less than or equal to 28 an d t less than or equal to 8 is given. (C) 1999 Elsevier Science B.V. All ri ghts reserved.