Guo, Wenbin, and Kar-Ping Shum. “Minimal Formations of Universal Algebras”. Discussiones Mathematicae - General Algebra and Applications, vol. 21, no. 2, 2001, p. 201, https://doi.org/10.7151/dmgaa.1037.
Guo, W., & Shum, K.-P. (2001). Minimal formations of universal algebras. Discussiones Mathematicae - General Algebra and Applications, 21(2), 201. https://doi.org/10.7151/dmgaa.1037
Guo W, Shum KP. Minimal formations of universal algebras. Discussiones Mathematicae - General Algebra and Applications. 2001;21(2):201.