Chihiro Suetake The Existence of a Symmetric Transversal Design <i>STD</i><sub>7</sub>[21; 3]. 525-528 2005 37 Des. Codes Cryptogr. 3 https://doi.org/10.1007/s10623-004-4041-x db/journals/dcc/dcc37.html#Suetake05a