mjhjmtu

does any know how I can create a command that places a symbol given as an argument inside cup?

For instance, the command uplus has the symbol '+' inside cup.
I would like to be able to place any given symbol inside cup (in special, the letter 'k').
An important issue is that the size of the symbol must respect the superscript math mode. Actually, the size of this symbol has to be a bit smaller, so as is '+' inside cup in uplus.

The figure below explains better what I am talking about.

I would like to obtain something similar to the second (from left to right) case.

Thanks in advance!

The stackinset command froom stackengine can do that:

documentclass[border = 2pt]standalone

 usepackagestackengine %
newcommandcupkstackMathstackinsetc0exc0.2exscriptscriptstyle kscriptstylecup

begindocument

$B^cupk $

enddocument 

We need fully scalable fonts for this, so fix-cm if the document is in the standard Computer Modern font. It is not necessary if other fonts are chosen.

RequirePackagefix-cm
documentclassarticle
usepackageamsmath

makeatletter
DeclareRobustCommandvcup[1]%
 mathbinvphantomcupmathpalettevcup@#1%

newcommandvcup@[2]%
 ooalign%
 $m@th#1cup$cr
 hidewidth
 raisebox%
 dimexprdepth+demote@#1dimexpr1.5ptrelaxrelax
 fontsizedemote@#1dimexprf@size ptz@selectfontcheck@mathfonts
 $m@th#2$%
 hidewidthcr
 %

newcommanddemote@[1]%
 ifx#1displaystyle 0.7
 elseifx#1textstyle 0.7
 elseifx#1scriptstyle 0.5
 else 0.4fififi

makeatother

begindocument

$AvcupkB^vcupk$

$uplusscriptstyleuplusscriptscriptstyleuplus$
$vcupkscriptstylevcupkscriptscriptstylevcupk$
$vcupyscriptstylevcupyscriptscriptstylevcupy$
$vcupgscriptstylevcupgscriptscriptstylevcupg$

enddocument