等方二次形式Florida. Tsit Yuen Lam (1973) Algebraic Theory of Quadratic Forms, §1.3 Hyperbolic plane and hyperbolic spaces, W. A. Benjamin. Tsit Yuen Lam (2005) Introduction
半原始環product ではない(Lam 1995, p. 42)。 Jacobson, Nathan (1989), Basic algebra II (2nd ed.), W. H. Freeman, ISBN 978-0-7167-1933-5 Lam, Tsit-Yuen (1995), Exercises