Algebraic Number Theory
《Algebraic Number Theory》 · 第 373 页 · Section 11.2「Exceptional zeros」, Theorem 11.14
Theorem 11.14 (Siegel) For each positive number $\varepsilon$ there is a positive constant $C(\varepsilon)$ such that if $\chi$ is a quadratic character modulo $q$, then $L(1,\chi)>C(\varepsilon)q^{-\varepsilon}$.