# mathstackers

## mathstackers

ConTeXt has a nice structure called `mathstackers`

in order to define new math commands in which some characters are stacked over another one. For more information refer to math-stc.mkiv.

The two command `\mathover[symbol]{}{`

} and `\mathunder[symbol]{}{`

} are built and can be used directly. However one may define one's own commands.

A typical example is when you want to put a small circle on top of a letter (as one would when defining the topological interior of a set…).
To do so we define first a new stacker named here `MySymbol`

, and then invoking that with `\definemathover`

we define two new commands `\interior`

and `\mystarred`

which can be used in math mode.

\definemathstackers[MySymbol] [voffset=-.3\mathexheight, hoffset=\zeropoint, mathclass=ord, topoffset=.4\mathemwidth, % poor man's italic correction middlecommand=\mathematics] \definemathover[MySymbol][interior]["2218] %this a small circle \definemathover[MySymbol][mystarred]["2717] % this is an asterisk \starttext Here is the new command \type{\interior{K}}: $\interior{K}$. Compare this to \type{\mathring{K}}: $\mathring{K}$. Here is the new command \type{\mystarred{K}}: $\mystarred{K}$. Here are the built-in commands \type{\mathover} and \type{\mathunder}: $\mathover[symbol]{"2217}{A}$, % 2217 is an asterisk $\mathover[symbol]{"2218}{A}$, % 2218 is a circle $\mathover[symbol]{"2219}{A}$, % 2219 is a bullet $\mathunder[symbol]{"2217}{A}$, $\mathunder[symbol]{"2218}{A}$, $\mathunder[symbol]{"2219}{A}$. \stoptext

When typeset in `mkiv`

one can see that the command `\interior{K`

} shows the letter K with a small circle above it.