A badly expanding set on the $2$-torus

Abstract

We give a counterexample to a conjecture stated in Linial and London 2006 regarding expansion on $\mathbb{T}^2$ under $\begin{bmatrix}1&1\\ 0&1\end{bmatrix}$ and $\begin{bmatrix}1&0\\ 1&1\end{bmatrix}$.