SUP, INF
inf = infimum：表示一个集合最大的下界
sup = supremum：表示一个集合最小的上界
RSS, SSR, SSE
In statistics, the residual sum of squares (RSS), also known as the sum of squared residuals (SSR) or the sum of squared errors of prediction (SSE), is the sum of the squares of residuals (deviations predicted from actual empirical values of data)
MSE, MSED
In statistics, the mean squared error (MSE) or mean squared deviation (MSD) of an estimator (of a procedure for estimating an unobserved quantity) measures the average of the squares of the errors—that is, the average squared difference between the estimated values and what is estimated.
Total Variation Distance
The total variation distance between two probability measures $P$ and $Q$ on a sigma-algebra $\mathcal{F}$ of subsets of the sample space $\Omega$ is defined via:
