A transversal design of order n and block size k, or TD(k; n), is a triple (X, G, B ), where X is a set of kn elements. G 5 hG1 , . . . , Gkj is a partition of X into k sets each of size n; each class of the partition is a group. B is a set of k-subsets of X, with the property that each B [ B satisfies uB > Giu 5 1 for each 1 # i # k; sets in B are blocks. Finally, each unordered pair of elements in X occurs together either in a group or in a single block, but not both.