Test
$\displaystyle \int^\frac{\pi}{4} _0 \cos(4x)$
. . . . . . . . . .$\displaystyle \setbox0=\hbox{$\text{o o} \atop\displaystyle \smile$}\dimen0=\wd0 \divide\dimen0 by 2
\advance\dimen0 by -12pt \lower2pt\hbox
to0pt{\kern\dimen0\Huge$\bigcirc$\hss}\box0$
(A few years ago, I had to develop a macro for putting a circle round an expression, when I was teaching a course on games theory. The solutions sheets for the homework exercises had to include things like $\displaystyle \begin{bmatrix}1&\framebox[1.25em]{$-1$}&\setbox0=\hbox{$-3$}\dimen0=\wd0 \divide\dimen0 by 2
\advance\dimen0 by -8.5pt \lower0.6pt\hbox to0pt{\kern\dimen0\Large$\bigcirc$\hss}\box0\,\\ \,\fbox{2}&\setbox0=\hbox{$-2$}\dimen0=\wd0 \divide\dimen0 by 2
\advance\dimen0 by -8.5pt \lower0.6pt\hbox
to0pt{\kern\dimen0\Large$\bigcirc$\hss}\box0&\fbox {3}\end{bmatrix}$.)
Haha the last 2 are nice ones !
Hmmm $\displaystyle \textcircled{L}\textcircled{e}\textcircled{t}\text circled{t}\textcircled{e}\textcircled{r} ~ \textcircled{b}\textcircled{y} ~\textcircled{l}\textcircled{e}\textcircled{t}\tex tcircled{t}\textcircled{e}\textcircled{r}$
$\displaystyle \begin{matrix}\Omega\times\Omega & \xrightarrow[\quad\quad\quad]{\alpha} & \Omega\\ ^{\pi\times\pi}\bigg\downarrow & & \bigg\downarrow ^{\pi} \\ \text{Top }\Omega\times\text{Top }\Omega & \xrightarrow[\quad\quad\quad]{\overset{\sim}{\alpha}} & \text{Top }\Omega\end{matrix}$
Nice! The only improvement I can suggest is a little tweak to lower the $\displaystyle \pi$ beside the right-hand vertical arrow:
$\displaystyle \begin{matrix}\Omega\times\Omega & \xrightarrow[\quad\quad\quad]{\alpha} & \Omega\\ ^{\pi\times\pi}\bigg\downarrow & & \bigg\downarrow {}^{\pi} \\ \text{Top }\Omega\times\text{Top }\Omega & \xrightarrow[\quad\quad\quad]{\overset{\sim}{\alpha}} & \text{Top }\Omega\end{matrix}$
Yeah, I meant to lower it. Thanks for the tip!
Do you have any idea how to do triangular diagrams with this? I can't figure out how to make it nice. One of my main problems is that [tex]\bigg\searrow[/tex] produces $\displaystyle \bigg\searrow$
Yeah, I'm not sure
Looking at this again, I can see another way in which it needs tweaking. Ideally, the vertical arrow on the left should be aligned with the product signs above and below it; and the vertical arrow on the right should similarly be aligned under the $\displaystyle \Omega$ above it. You can achieve that quite easily by using the \llap and \rlap commands. These produce boxes of zero width whose contents overlap to the left or right respectively.
$\displaystyle \begin{matrix}\Omega\times\Omega & \xrightarrow[\quad\quad\quad]{\alpha} & \Omega\\ \llap{$\scriptstyle\pi\times\pi$}\bigg\downarrow & & \bigg\downarrow\rlap{$\scriptstyle\pi$} \\ \text{Top }\Omega\times\text{Top }\Omega & \xrightarrow[\quad\quad\quad]{\overset{\sim}{\alpha}} & \text{Top }\Omega\end{matrix}$
Yes, that is an artefact caused by the fact that TeX does not have ready-made glyphs for long horizontal arrows. Instead, it constructs them on the fly by joining a sequence of short dashes to an arrowhead. The effect on the screen looks a bit uneven, though the printed version would probably be smoother.