The Arithmetic of Elliptic Curves
《The Arithmetic of Elliptic Curves》 · 第 127 页 · Chapter IV，Section 5「The Formal Logarithm」，Definition
Let $R$ be a torsion-free ring, let $K=R\otimes\mathbb Q$, let $F/R$ be a formal group, and let $\omega(T)$ be the normalized invariant differential on $F/R$. The formal logarithm of $F/R$ is the power series $\log_F(T)=\int\omega(T)\in K[[T]]$.