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We can use \llbracket and \rrbracket (provided by the stmaryrd package) to generate double brackets. My questions are:

  • how we can generate double-struck parentheses in the same style as the single-struck bracket version?
  • how we can generate double-struck parentheses such that we can write two elements vertically (like the vector format)?

Two things are important:

  1. The distance between two parenthesis which should be as nice as in the \llbracket \rrbracket.

  2. The top and bottom of the two parenthesis should touch each other like \llbracket \rrbracket.

Edit: This question in some aspects can be the counterpart for this question replacing by parenthesis.

11
  • Would $\llparenthesis x \rrparenthesis$ or $\left(\!\left(\frac{1}{\frac{1}{2}}\right)\!\right)$ work? Jul 14, 2020 at 2:29
  • @M.AlJumaily: Thanks. Not actually. The one created by '\llbracket \rrbracket' is very neat. I need to have something in that style.
    – Amin
    Jul 14, 2020 at 2:33
  • 4
    sure! maybe you should include a sample image of how you would like the result to look like. You can hand-draw it (be precise please). Jul 14, 2020 at 2:35
  • 2
    Does this answer your question? Double square brackets
    – Thruston
    Jul 14, 2020 at 7:37
  • 1
    I'm not aware of the existence of any double-struck round parentheses that can be scaled via \left and \right directives. In this regard, the macros \llparenthesis and \rrparenthesis of the stmaryrd or stix packages are very different from \llbracket and \rrbracket.
    – Mico
    Jul 15, 2020 at 18:50

1 Answer 1

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You can load a double-struck or outline font of your choice and use its symbols as delimiters.

\documentclass{article}
\tracinglostchars=2
\usepackage{unicode-math}

% Font available from:
% https://www.fontsquirrel.com/fonts/library-3-am
\setfontface\outline{LIBRARY 3 AM}[
  Scale=MatchUppercase]
  
\newcommand\llparen{\mathopen{\textnormal{\outline (}}}
\newcommand\rrparen{\mathclose{\textnormal{\outline )}}}
\newcommand\llbrack{\mathopen{\textnormal{\outline [}}}
\newcommand\rrbrack{\mathclose{\textnormal{\outline ]}}}
\newcommand\llbrace{\mathopen{\textnormal{\outline \textbraceleft}}}
\newcommand\rrbrace{\mathclose{\textnormal{\outline \textbraceright}}}

\newcommand\Parens[1]{%
  \llparen%
  #1%
  \rrparen}

\newcommand\Brackets[1]{%
  \llbrack%
  #1
  \rrbrack}
  
\newcommand\Braces[1]{%
  \llbrace%
  #1%
  \rrbrace}

\pagestyle{empty} % Format the MWE for TeX.SX

\begin{document}
\begin{gather*}
 \llbrace\llbrack\llparen \mathbb R \rrparen\rrbrack\rrbrace \\
 \Braces{\Brackets{\Parens{\mathbb C}}}
\end{gather*}
\end{document}

Library 3AM sample

This template does not enable scaling, which would be much more complicated. Unfortunately, although you can set a blackboard font with \setmathfontface, unicode-math will not substitute it for (), {} or [].

You could, however, define \bigllparen, \biggrrbrace, etc., which scale the delimiters, and build size-changing commands from that.

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