TeX source:

\left\{\begin{matrix} x \in [\tilde{x}, \tilde{x} + \beta^{-2}] \; \; \mathrm{truncation} \\ x \in [\tilde{x}-\frac{1}{2}\beta^{-t}, \tilde{x}+\frac{1}{2}\beta^{-t}] \: \: \mathrm{rounding} \end{matrix}\right.