1. D. N. Ivanov, “Orthogonal decompositions of associative algebras, and balanced systems of idempotents,” Mat. Sb. [Russian Acad. Sci. Sb. Math.], 189 (1998), no. 12, 83–102.
2. A. I. Kostrikin, I. A. Kostrikin, and V. A. Ufnarovskii, “Orthogonal decompositions of simple Lie algebras (type An).,” Trudy Mat. Inst. Steklov [Proc. Steklov Inst. Math.], 158 (1981), 105–120.
3. T. Beth, D. Jungnickel, and H. Lenz, Design Theory, 2nd edn, Cambridge University Press, Cambridge, 1999.
4. D. N. Ivanov, “Orthogonal decompositions of semisimple associative algebras,” Vestnik Moskov. Univ. Ser. I Mat. Mekh. [Moscow Univ. Math. Bull.], 43 (1988), no. 1, 9–14.
5. A. I. Kostrikin and Huu Tiep. Pham, Orthogonal Decompositions and Integral Lattices, Walter de Gruyter, Berlin, 1994.