Let $X$ be a thick building with a system of apartments $\mathcal A$. I've been trying to understand a proof in the theorem of these notes (http://www-users.math.umn.edu/~garrett/m/buildings/book.pdf), page 55. I am not sure whether the argument in the proof is correct. Sorry to not make my po...

Let $m$ and $n$ be two integers such that $m>n$. Then find the number of integers less than $m$ and relatively prime to $n$. I had come across a problem of this type with specific values for $m$ and $n$, unfortunately, the values I don't remember anymore. So I asked this general question. H...