Frans Oort and Thomas Zink

摘要

Let $X$ be a $p$-divisible group with constant Newton polygon over a normal Noetherian scheme $S$. We prove that there exists an isogeny $X o Y$ such that $Y$ admits a slope filtration. In case $S$ is regular this was proved by N. Katz for dim $S = 1$ and by T. Zink for dim $S geq 1$.