hould satisfy the following property: for any pair of disjoint subsamples <span class="math inline">\(\mathcal{S}=\{\mathbf{x}_i\}\)</span> and <span class="math inline">\(\mathcal{S}'=\{\mathbf{x}_{i'}\}\)</span>, the distributions of the pair of subsamples <span class="math inline">\(F_\mathcal{S}\)</span> and <span class="math inline">\(F_{\mathcal{S}'}\)</span> should not differ by too much: <span class="math display">\[\begin{equation}
d(F_\mathcal{S},F_{\mathcal{S}'}) \approx 0,\label{eq:1}
\end{equat