Let $\lambda>\omega$ a cardinal. We know that there is a bijection $\pi$ between $\lambda^+$ and $\lambda\times\lambda^+$. I don't understand in Remark 1 of the paper Shelah's proof of diamond of Komjath the words : "a club set of $\delta<\lambda^+$ (do we take a $C\subset\delta$ club in $\delta$ ? or ... ?)" $\pi$ is a bijection from $\delta$ onto $\lambda\times\delta$ " (why ?) Thanks a lot.