> Fabrice Couvreur <mailto:fabrice1.couvreur@gmail.com>
> 15. Juni 2016 um 14:48
> Hi Wolfgang,
> what directory I put this file knowing that I installed the standalone 
> version in /home/fab/context
> Fabrice
>
The commend was meant for Hans, all *you* have to do is update your TeX 
installation, afterwards you can try the following example:

\useMPlibrary[mat]

\setupmathstackers
   [both]
   [color=darkred,
    alternative=mp]

\setupmathstackers
   [top]
   [color=darkred,
    alternative=mp]

\setupmathstackers
   [bottom]
   [color=darkred,
    alternative=mp]

\starttext

$\overbracket   {a+b+c+d} \quad \underbracket    {a+b+c+d} \quad 
\doublebracket{a+b+c+d}$ \blank
$\overparent    {a+b+c+d} \quad \underparent     {a+b+c+d} \quad 
\doubleparent {a+b+c+d}$ \blank
$\overbrace     {a+b+c+d} \quad \underbrace      {a+b+c+d} \quad 
\doublebrace  {a+b+c+d}$ \blank
$\overbar       {a+b+c+d} \quad \underbar        {a+b+c+d} \quad 
\doublebar    {a+b+c+d}$ \blank

$\overleftarrow  {a+b+c+d} \quad \overrightarrow  {a+b+c+d} $ \blank
$\underleftarrow {a+b+c+d} \quad \underrightarrow {a+b+c+d} $ \blank

\stoptext

Wolfgang