TeX source:

\left\{\begin{array}{l} \text { distance between the } \\ \text { Riemann sum and } \\ \text { the exact area } \end{array}\right\} \leq\left\{\begin{array}{l} \text { distance between the } \\ \text { upper sum and } \\ \text { the lower sum } \end{array}\right\} \leq\{\mathrm{f}(\mathrm{b})-\mathrm{f}(\mathrm{a})\} \cdot(\text { mesh of } \mathrm{P})