1. A. Ehrenfeucht, J. Karhumäki, and G. Rozenberg. The (generalized) Post correspondence problem with lists consisting of two words is decidable. Theoretical Computer Science, 21(2):119–144, 1982.
2. M. Garey and D. Johnson. Computers and Intractability: A Guide to the Theory of NP-Completeness. W. H. Freeman, 1979.
3. Lect Notes Comput Sci;T. Harju,1996
4. Y. Lecerf. Récursive insolubilité de l’équation générale de diagonalisation de deux monomorphisms de monoïdes libres φx = Ψx. Comptes Rendus Acad. Sci. Paris, 257:2940–2943, 1963.
5. Y. Matiyasevich and G. Sénizergues. Decision problems for semi-Thue systems with a few rules. In Proceedings of the 11th IEEE Symposium on Logic in Computer Science, pages 523–531, 1996.