User:Tsinpeng Lee/Sandbox

Oh, let me type in something like this
 * $g_n = \displaystyle\sum_{k=0}^{n 2^n - 1} \frac{k}{2^n} I_{\left[\frac{k}{2^n} < f^{+} < \frac{k+1}{2^n}\right]} + nI_{\left[f^{+}\geq n \right]}$.

Ahh, and what IS that????