I did not know if it would be this easy, but it turned out so. I took my revised answer at Really wide hat symbol for \reallywidehat
and made two simple changes:
I changed all occurences of "hat" to "check"
I changed the final \stackon
argument from \tmpbox
to \scalebox{-1}{\tmpbox}
.
That was it. Here it is:
\documentclass{article}
\usepackage{scalerel,stackengine}
\stackMath
\newcommand\reallywidecheck[1]{%
\savestack{\tmpbox}{\stretchto{%
\scaleto{%
\scalerel*[\widthof{\ensuremath{#1}}]{\kern-.6pt\bigwedge\kern-.6pt}%
{\rule[-\textheight/2]{1ex}{\textheight}}%WIDTH-LIMITED BIG WEDGE
}{\textheight}%
}{0.5ex}}%
\stackon[1pt]{#1}{\scalebox{-1}{\tmpbox}}%
}
\parskip 1ex
\begin{document}
$\reallywidecheck{zbcdefghijklm}$
$\reallywidecheck{zbcdefghijk}$
$\reallywidecheck{zbcdefghi}$
$\reallywidecheck{zbcdefg}$
$\reallywidecheck{zbcde}$
$\reallywidecheck{zbc}$
$\reallywidecheck{zb}$
$x\cdot\reallywidecheck{a_1+a_2}\cdot y$
\end{document}

Best of all, it avoids the use of mathabx
, which resets a lot of math symbols.
beamer
? If not, please use this answer of the post you have linked to: tex.stackexchange.com/a/44277 . Why have you tagged latex3e? – LaRiFaRi Jun 9 '15 at 11:28mathabx
. – Steven B. Segletes Jun 9 '15 at 11:31