Hristov, Asen, and Georgi Kostadinov. 2016. “MANIFOLDS ADMITTING A STRUCTURE OF FOUR DIMENTIONAL ALGEBRA OF AFFINORS”. Ann. Sofia Univ. Fac. Math. And Inf. 103 (December):89-95. https://ftl5.uni-sofia.bg./index.php/fmi/article/view/57.