Diane Donovan Abdollah Khodkar Anne Penfold Street Doubling and Tripling Constructions for Defining Sets in Steiner Triple Systems. 65-89 2003 19 Graphs and Combinatorics 1 http://dx.doi.org/10.1007/s00373-002-0485-9 db/journals/gc/gc19.html#DonovanKS03