Naive Lie Theory
《Naive Lie Theory》 · 印刷第 215 页 Section 12.2「Complements on quotients」，12.2.6 首句的同源定义
As in 9.6.1 (where the groups were reductive) we say that a homomorphism of connected algebraic groups $\phi:G\to G'$ is an isogeny if it is surjective and has finite kernel.