1. K. Ambos-Spies, On the structure of the recursively enumerable degrees, Dissertation, Universität München, 1980.
2. K. Ambos-Spies, On pairs of recursively enumerable degrees, Trans. Amer. Math. Soc. 283 (1984) 507–531.
3. K. Ambos-Spies, Contiguous r.e. degrees, in Proceedings of Logic Colloquium 83, Springer Lecture Notes in Mathematics, 1104 (1984) 1–37.
4. K. Ambos-Spies and M. Lerman, Lattice embeddings into the recursively enumerable degrees, to appear.
5. P.A. Fejer, The density of the nonbranching degrees, Ann. Math. Logic 24 (1983) 113–130.