# Getting a scalable symbol from fdsymbol package

The general answers how to import symbols from packages are difficult to understand for beginners. I have been unsuccessful in adapting existing answers to import scalable symbol \lBrack and rBrack from FdSymbol package. I have this for the smallest symbol

    \documentclass{article}

\DeclareFontFamily{U}{FdSymbolF}{}
\DeclareFontShape{U}{FdSymbolF}{m}{n}{<-> s * FdSymbolF-Book}{}
\DeclareSymbolFont{fdbrackets}{U}{FdSymbolF}{m}{n}
\DeclareMathSymbol{\lBrack}{\mathord}{fdbrackets}{"60}
\DeclareMathSymbol{\rBrack}{\mathord}{fdbrackets}{"66}

\begin{document}

$\lBrack x,y \rBrack$

\end{document}


But, how do I make it scalable using \Bigl \Bigr? I would appreciate any help.

\documentclass{article}
\DeclareFontFamily{U}{FdSymbolF}{}
\DeclareFontShape{U}{FdSymbolF}{m}{n}{<-> s * FdSymbolF-Book}{}
\DeclareSymbolFont{fdbrackets}{U}{FdSymbolF}{m}{n}
\DeclareMathDelimiter{\lBrack}{\mathopen}{fdbrackets}{"60}{fdbrackets}{"60}
\DeclareMathDelimiter{\rBrack}{\mathclose}{fdbrackets}{"66}{fdbrackets}{"66}
\begin{document}

$\lBrack x,y \rBrack$
$\Bigl\lBrack x,y \Bigr\rBrack$

\end{document}


However, using a special math package or lualatex/xelatex make things easier:

\documentclass{article}
\usepackage{unicode-math}
\setmathfont{XITS Math}
\begin{document}

$\lBrack x,y \rBrack$
$\Bigl\lBrack x,y \Bigr\rBrack$

\end{document}


• Thank you very much. The first answer works well. I was not able to get the second answer to work in a slightly more complicated setting. For example, it seems that LuaLaTeX does not recognize the command \ker. When I tried to redefine it, LuaLaTeX did not accept the new definition. Feb 16, 2018 at 16:25