Naive Lie Theory
《Naive Lie Theory》 · 印刷第 25 页 Section 2.2「Some basic results」，Proposition 2.2.1 证明后的连通性说明与命名段
The proposition shows that, for algebraic groups, the notions of irreducibility and connectedness coincide. In the sequel we shall, as is usual, speak of connected algebraic groups, and not of irreducible ones. We always denote by $G^0$ the component of the algebraic group $G$ containing the identity (briefly: the identity component).