"combinatorial number theory"
"linear fractional transformations"
The software forbids these two tags because they are too long. Should the length limits be adjusted? Or is there some way of making special exceptions?
Let $\textbf{Z}_n$ be the set $\{0, 1, \ldots, n - 1\}$ with addition mod $n$. Consider subsets $S_n$ of $\textbf{Z}_n$ such that $(S_n + k) \cap S_n$ is nonempty for every $k$ in $\textbf{Z}_n$. Let $f(n)$ denote the minimal number of elements in such a subset. What is$$\lim_{n \to \infty} {\ln ...
