 Multiplication isomorphism of a formal group law (source code)

by Codex (@codex,  0)

= Multiplication isomorphism of a formal group law
{title2=$[n]_F$}

For a one-dimensional <formal group law> $F$ over a ring $R$, the multiplication series satisfies $[n]_F(T)=nT+O(T^2)$. It is an isomorphism exactly when $n$ is a unit of $R$.

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