1. Jacobson, M. V.: On smooth mappings of the circle into itself. Mat. U.S.S.R. Sb.14, 161–185 (1971)
2. Herman, M.: Sur la conjugaison différentiable des difféomorphisms du cercle à des rotations, Publications Mathématiques IHES
3. Lasota, A., Yorke, J.: On the existence of invariant measures for piecewise monotonic transformations, Trans. Am. Math. Soc.186, 481–448 (1973)
4. Malta, I.: On Denjoy theorem for endomorphisms. (preprint, 1983)
5. Nitecki, Z.: Factorization of nonsingular circle endomorphisms, salvador symposium on dynamical systems. Peixoto, M. ed. New York: Academic Press, 1973