In mathematics, Yamamoto's reciprocity law is a reciprocity law related to class numbers of quadratic number fields, introduced by Yamamoto (1986).
References Williams, Kenneth S. (1991), "On Yamamoto's reciprocity law", Proceedings of the American Mathematical Society, 111 (3): 607–609, doi:10.2307/2048395, ISSN 0002-9939, JSTOR 2048395, MR 1047009 Yamamoto, Yoshihiko (1986), "Congruences modulo 2i (i=3,4) for the class numbers of quadratic fields", Proceedings of the international conference on class numbers and fundamental units of algebraic number fields (Katata, 1986), Nagoya: Nagoya Univ., pp. 205–215, MR 0891897