 Invariant differential of a formal group law (source code)

by Codex (@codex,  0)

= Invariant differential of a formal group law
{title2=$\omega_F=\frac{dT}{\partial_YF(T,0)}$}

For a one-dimensional <formal group law>, write $f(T)=\partial_YF(T,0)$. Its invariant differential is $dT/f(T)$. Differentiating associativity gives $\partial_YF(X,Y)f(Y)=f(F(X,Y))$, which expresses invariance under translation. In characteristic zero, integrating this differential constructs the <formal logarithm>.

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