how to type '<<'?

I am translating a book into Chinese, and it doesn't provide the latex file of the book. How to type ‘<<’ and '>>' as followed?

$$\ll \mathbf{A},\mathbf{B} \gg = \ll \mathbf{A} \gg \ll \mathbf{B} \gg + \ll \mathbf{B},\mathbf{A} \gg$$


'\ll' and '\gg' seem to be wider...

• \langle\langle A\rangle\rangle... – TeXnician Oct 15 '17 at 9:06
• oh,thank! Finally I use '\langle\!\langle A\rangle\!\rangle' – Zerolover Oct 15 '17 at 9:19
• I've put it into an answer. Feel free to accept ;) – TeXnician Oct 15 '17 at 9:23

The symbol is available with MnSymbol:

\documentclass{article}
\usepackage{amsmath}

\DeclareFontFamily{OMX}{MnSymbolE}{}
\DeclareFontShape{OMX}{MnSymbolE}{m}{n}{
<-6>  MnSymbolE5
<6-7>  MnSymbolE6
<7-8>  MnSymbolE7
<8-9>  MnSymbolE8
<9-10> MnSymbolE9
<10-12> MnSymbolE10
<12->   MnSymbolE12}{}
\DeclareSymbolFont{mnlargesymbols}{OMX}{MnSymbolE}{m}{n}
\SetSymbolFont{mnlargesymbols}{bold}{OMX}{MnSymbolE}{b}{n}
\DeclareMathDelimiter{\llangle}{\mathopen}{mnlargesymbols}{'164}{mnlargesymbols}{'164}
\DeclareMathDelimiter{\rrangle}{\mathclose}{mnlargesymbols}{'171}{mnlargesymbols}{'171}

\begin{document}

$\llangle \mathbf{A} \rrangle$
$\bigl\llangle \mathbf{A} \bigr\rrangle$
$\Bigl\llangle \mathbf{A} \Bigl\rrangle$
$\biggl\llangle \mathbf{A} \biggr\rrangle$
$\left\llangle \dfrac{\mathbf{A}}{2} \right\rrangle$

\end{document}


Just to put it as answer: You are not asking for <, but for an angled brace. You can accomplish this in LaTeX using \langle for the left one and \rangle for the right one.

As it is not the intended use to put two of them next to each other, the spacing is probably rather bad, but you can influence it using the usual math spacing commands. Maybe you want to define your own command for that.