1. APERY, R.: Sur les branches superlinéaires des courbes algebriques. C. R. Acad. Sci. Paris 222, 1198?1200 (1946).
2. BRESINSKY, H.: Semigroup and analytic equivalence of algebroid branches in the plane. Thesis, Arizona State University, Tempe, Arizona (1969).
3. BRESINSKY, H.: On prime ideals with generic zero $$x_i = t^{n_i }$$ . Proc. Amer. Math. Soc. 47, 329?332 (1975).
4. HERZOG, J.: Generators and relations of abelian semigroups and semigroup rings. manuscripta math. 3, 175?193 (1970).
5. WATANABE, K.: Some examples of one dimensional Gorenstein domains. Nagoya Math. J. 49, 101?109 (1973).