We calculate
by evaluating the syntomic cohomology
introduced by Bhatt, Morrow and Scholze. This recovers calculations of Hesselholt,
Madsen and Speirs and generalizes an example of Mathew treating the case
and
. Our main
innovation is systematic use of the floor and ceiling functions, which clarifies matters substantially
even for
.
We furthermore observe a persistent phenomenon of
slopes. As an application, we
answer some questions of Hesselholt.