1. [A] S. Abhyankar,On semigroup of a meromorphic curve, Tokyo, Kinokuniya Book-Store, 1978.
2. [C] P. Cohn,Free Rings and Their Relations, second edition, Academic Press, New York, 1985.
3. [D] A. Dimca,Hypersurfaces in ℂ2n diffeomorphic to ℝ4n− (n≥2), Max-Plank Institute, preprint, 1990.
4. [G] A. Gutwirth,The action of an algebraic torus on the affine plane. Transactions of the Amercaan Mathematical Society105 (1962), 407–414.
5. [I] S. Titaka,On Kodaira logarithmic dimension of algebraic varieties, inComplex Analysis and Algebraic Geometry, Iwanami, Tokyo, 1977, pp. 175–189.