On quasi-symmetric 2-(28, 12, 11) and 2-(36, 16, 12) designs
The authors construct 21 non-isomorphic quasi-symmetric 2-\((28,12,11)\) designs, 18 of which do not have the symmetric difference property (which says that the symmetric difference of any two blocks is either a block or the complement of a block). These are the first examples of non-SDP quasi-symmetric designs of derived type. They also obtain 28 non- isomorphic non-SDP quasi-symmetric 2-\((36,16,12)\) designs.
scientific article; zbMATH DE number 722117