\Bibitem{Kem81} \by A.~R.~Kemer \paper Decomposition of varieties \jour Algebra Logika \yr 1981 \vol 20 \issue 4 \pages 395--418 \mathnet{http://mi.mathnet.ru/al1735} \mathscinet{https://mathscinet.ams.org/mathscinet-getitem?mr=663058}