Wide inverted breve overset

Question

I want an inverted breve that spans the width of two symbols rather than one.

I have tried the suggestions in: inverted breve accent in math mode , and in How to put \smallsmile or \smallfrown on top of a letter.

But these were meant for inverted breve oversets that only span the width of one symbol.

Those suggestions give the top result below, whereas what I want is the bottom result below:

What is the best way to do this ?

Answer 1

You can use yhmath:

\documentclass{article}
\usepackage{yhmath}
\begin{document}
$\wideparen{\Delta k}+\wideparen{x+y+z}$
\end{document}

This changes the math extension symbol font, so you may not want to do it; in this case you can just import the needed math accent

\documentclass{article}

\DeclareSymbolFont{YHlargesymbols}{OMX}{yhex}{m}{n}
\DeclareMathAccent{\wideparen}{\mathord}{YHlargesymbols}{"F3}

\begin{document}
$\wideparen{\Delta k}+\wideparen{x+y+z}$
\end{document}

Answer 2

Not exactly a parenthesis but...

\documentclass{article}
\usepackage{abraces}
\begin{document}
\[
  \aoverbrace[L1R]{\triangle k}_{} \quad
  \aoverbrace[L1R]{\triangle k \nabla}_{}  \quad
  \aunderbrace[l1r]{\triangle k}_{}
\]
\end{document}

Answer 3

In this case, I use stackengine package (\stackon) to stack the overset with the proper vertical separation, and the scalerel package (\hstretch) to horizontally stretch the \smallfrown to double its original width. Increasing the 2 argument will make the overset wider still.

\documentclass{article}
\usepackage{scalerel}
\usepackage{stackengine}
\usepackage{MnSymbol}
\stackMath
\begin{document}
\( \stackon[0pt]{\Delta k}{\hstretch{2}{\smallfrown}} \)
\end{document}

Here I show a wider alternative, also more rounded, and set lower upon the symbol:

\documentclass{article}
\usepackage{scalerel}
\usepackage{stackengine}
\usepackage{MnSymbol}
\stackMath\def\useanchorwidth{T}
\begin{document}
\( \stackon[-2.1pt]{\Delta k}{\vstretch{1.3}{\hstretch{2.9}{\smallfrown}}} \)
\end{document}