| Example 1 | Example 3 | other reference |
\begin{tabular}{|c||ccc||r|}
\hline
\textbf{\em k} & $x_1^k$ & $x_2^k$ & $x_3^k$ & remarks \\
\hline \hline
0 & -0.30000000 & 0.60000000 & ~0.70000000 & $x^0$ \\
1 & ~0.47102965 & 0.04883157 & -0.53345964 & \\
2 & ~0.49988691 & 0.00228830 & -0.52246185 & \\
3 & ~0.49999976 & 0.00005380 & -0.52365600 & $\epsilon<\delta$ \\
4 & ~0.50000000 & 0.00000307 & -0.52359743 & ($\forall n>N$) \\
\hline
7 & ~0.50000000 & 0.00000000 & -0.52359878 & $\epsilon\ll\zeta$ \\
\hline
\end{tabular}
|

Using the \hline macro twice (\hline\hline) after a row produces a horizontal double line across the table.