Ditchev, Angel. “SOME RESULTS ON THE UPPER-SEMILATTICE OF R.E. $m$-DEGREES INSIDE A SINGLE R.E. $tt$-DEGREE”. Ann. Sofia Univ. Fac. Math. and Inf. 96 (December 12, 2004): 23–34. Accessed November 25, 2024. https://annual.uni-sofia.bg/index.php/fmi/article/view/158.