由Lagrange展开产生的一对公式

Let Γ denote the ring of formal power series over the complex field C. Let φ∈Γ with φ(0)=0 and φ′(0)=0 So that it has a compositional inverse ψ with ψ(φ(t))=φ(ψ(t))=1. Then for every f∈Γ and α∈C With α≠0 we have Lagrange′s formal expansion