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2. Multi-set designs—designs having blocks with repeated elements;Assaf;Congr. Numer.,1985
3. Design with repeated elements in blocks: A survey and some recent results;Billington;Congr. Numer.,1989
4. The intersection problem for combinatorial designs;Billington;Congr. Numer.,1993
5. The intersection problem for K4−e designs;Billington;J. Statist. Plann. Inference,1997