Bojkova, Elka. 1995. “An Example of a Finite Number of Recursively Enumerable $m$-Degrees Containing an Infinite Sequence of Recursively Enumerable Sets”. Ann. Sofia Univ. Fac. Math. And Inf. 87 (December):223-34. https://ftl5.uni-sofia.bg./index.php/fmi/article/view/415.