V. H. Toghanyan, “SUBDIRECT INDECOMPOSABLE PARTIALLY COMMUTATIVE, NORMAL AND QUASI NORMAL ALGEBRAS”, Proc. YSU A: Phys. Math. Sci., vol. 37, no. 2 (201), pp. 30–37, Jun. 2003, doi: 10.46991/PYSUA.2003.37.2.030.