symbols
Possible Duplicate:
How to look up a symbol?
How does one make the symbol for a blackboard bold kind square brackets ,something like [[.The symbol being talked about is used for containing formulas whose truth values are being talked about in propositional logic.
Thanks and regards
An image of the symbol: 
You can build the symbols yourself.
\documentclass{article}
\usepackage{pict2e}
\makeatletter
\DeclareRobustCommand{\loplus}{\mathbin{\mathpalette\dog@lsemi{+}}}
\DeclareRobustCommand{\lotimes}{\mathbin{\mathpalette\dog@lsemi{\times}}}
\DeclareRobustCommand{\roplus}{\mathbin{\mathpalette\dog@rsemi{+}}}
\DeclareRobustCommand{\rotimes}{\mathbin{\mathpalette\dog@rsemi{\times}}}
\newcommand{\dog@rsemi}[2]{\dog@semi{#1}{#2}{-90,90}}
\newcommand{\dog@lsemi}[2]{\dog@semi{#1}{#2}{270,90}}
\newcommand{\dog@semi}[3]{%
\begingroup
\sbox\z@{$\m@th#1#2$}%
\setlength{\unitlength}{\dimexpr\ht\z@+\dp\z@\relax}%
\makebox[\wd\z@]{\raisebox{-\dp\z@}{%
\begin{picture}(1,1)
\linethickness{\variable@rule{#1}}
\roundcap
\put(0.5,0.5){\makebox(0,0){\raisebox{\dp\z@}{$\m@th#1#2$}}}
\put(0.5,0.5){\arc[#3]{0.5}}
\end{picture}%
}}%
\endgroup
}
\newcommand{\variable@rule}[1]{%
\fontdimen8
\ifx#1\displaystyle\textfont3\else
\ifx#1\textstyle\textfont3\else
\ifx#1\scriptstyle\scriptfont3\else
\scriptscriptfont3\relax
\fi\fi\fi
}
\makeatother
\begin{document}
$A\roplus B\rotimes C\loplus D \lotimes E$
$\scriptstyle \roplus\rotimes\loplus\lotimes$
\end{document}
However, note that the standard \oplus and \otimes are lighter than + and \times, so you may want to redefine also them in a similar way, using the full circle.
Best Answer
You are looking for
\llbracketand\rrbracketfrom thestmaryrdpackage\textlbrackdbland\textrbrackdblfrom thetextcomppackageDetexify is an online tool that can help you find latex symbols by drawing them.