symbols - Double square brackets - TeX - LaTeX Stack Exchange

\documentclass{article}
\usepackage{booktabs}% http://ctan.org/pkg/booktabs
\newcommand{\tabitem}{~~\llap{\textbullet}~~}
\begin{document}

\begin{table}
  \centering
  \begin{tabular}{lll}
    \toprule
    \multicolumn{3}{c}{Classification of the criticel point $(0,0)$ of $x' = Ax, |\mathbf{A}| \not= 0$.} \\[.5\normalbaselineskip]
    Types & Type of Critical Point & Stability \\
    \midrule
    1.~Real unequal eigenvalues of same sign \\
    \tabitem $\lambda_1 > \lambda_2 > 0$ & Improper node/node & Unstable \\
    \tabitem $\lambda_1 < \lambda_2 < 0$ & Improper node/node & Asym.~stable \\[.5\normalbaselineskip]
    2.~Real unequal eigenvalues of opposite sign \\
    \tabitem $\lambda_2 < 0 > \lambda_1$ & Saddle point & Unstable \\[.5\normalbaselineskip]
    3.~Equal eigenvalues \\ Subtype 1: Two Independent vectors \\
    \tabitem $\lambda_1 = \lambda_2 > 0$ & Proper node & Unstable \\
    \tabitem $\lambda_1 = \lambda_2 < 0$ & Proper node & Asym.~stable \\
    \bottomrule
  \end{tabular}
\end{table}

\end{document}

\documentclass{article}
\usepackage{stmaryrd}

\begin{document}

\begin{equation}
  \llbracket     1 \rrbracket       \quad
  \llparenthesis 2 \rrparenthesis   \quad
  \llceil        3 \rrceil          \quad
  \llfloor       4 \rrfloor         \quad
\end{equation}

\end{document}