In a paper, I want to prove a result that seems to me general.
Let $g:\delta\longrightarrow cf(\lambda)$ where $\delta$ is an ordinal less than $\lambda^+$ and $\lambda$ a cardinal. Suppose that $\forall i Remark : I think the notation $g^{-1}[i]$ means the inverse image that is $\{\alpha<\delta : g(\alpha)
We have $\delta=g^{-1}[cf(\lambda)]=\bigcup_{i Thanks.