Double-struck parentheses

Question

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:

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

Would $\llparenthesis x \rrparenthesis$ or $\left(\!\left(\frac{1}{\frac{1}{2}}\right)\!\right)$ work? — M. Al Jumaily, Jul 14 '20 at 02:29
@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 '20 at 02:33
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). — M. Al Jumaily, Jul 14 '20 at 02:35
@M.AlJumaily: I just described it. You can consider there is parenthesis instead of bracket in $\llbracket \rrbracket$ and could be vertical taking two elements like vector. — Amin, Jul 14 '20 at 02:38
Does this answer your question? Function of interpretation by assignment g — barbara beeton, Jul 14 '20 at 23:44
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 '20 at 18:50
A possible mechanism has been shown in this answer: https://tex.stackexchange.com/a/308980 If this is acceptable, it may be considered a duplicate. — barbara beeton, Jul 16 '20 at 04:39

score 3 · Answer 1 · answered Jul 15 '20 at 06:13

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}

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.

Double-struck parentheses

1 Answers1

Linked