Tahara refers to the "Gauss symbol" in the article, On the second cohomology groups of semidirect products, Math. Z. 129 (1972) 365--379.  For a fixed $n$, let $S_{ij}$ be the expression 
\begin{equation}
\left[ \frac{i+j}{n}\right] -\left[ \frac{i}{n}\right] -
\left[ \frac{j}{n}\right]
\end{equation} 
which comes up often in the paper.  What does $\left[ \text{  }\right] $ mean here?  Also, what then are $S_{k,-k}$ and $S_{k,k}$, assuming $k$ and $n$ are coprime?