# Ugly spacings with \mathcal font

I hate the horizontal spacings with letters from the \mathcal font. Is there a way to fix them? Here's a MWE showing the ugliness:

\documentclass[11pt,letterpaper,twoside]{book}
\usepackage[T1]{fontenc}
\usepackage{lmodern}
\usepackage{microtype}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{mathtools}
\usepackage{tensor}

\begin{document}

\begin{equation*}
dx_{\smash{\, \mathcal{AB}}}^{\mu} + dx_{\smash{\, \mathcal{BC}}}^{\mu} + dx_{\smash{\, \mathcal{CD}}}^{\mu} + dx_{\smash{\, \mathcal{DA}}}^{\mu} \ne 0.
\end{equation*}

\end{document}


Preview:

As the preview is showing, the A and D letters are getting some relatively large space between them, while A and B are glued together. I find this very ugly. Is there a way to make a nice consistent (i.e. uniform) spacing between each of these letters?

I'm tempted to add some space between A and B (and also between B and C), but that would be an "hack" and wouldn't be consistent.

Unrelated: I had to smash these letters and add a small space to make the indices at a consistent height with other equations, and to prevent the indices to overlap.

• You say doing doing the spacing manually would be a "hack", but you are already doing this when you write \, in the subscripts, so the odd \! is not much extra for that level of control over the spacing. Jul 13 '20 at 22:14

The correct way to kern characters in math mode is using \mkern. If you want to have this done automatically you will have to create a virtual font.

\documentclass{article}
\begin{document}
$dx_{\mathcal{AB}}^{\mu} + dx_{\mathcal{BC}}^{\mu} + dx_{\mathcal{C\mkern-1mu D}}^{\mu} + dx_{\mathcal{D\mkern-2mu A}}^{\mu} \ne 0.$
\end{document}


You can either:

• Load unicode-math and use an OpenType font
• Load unicode-math and load a different calligraphic font with \setmathfont[range=cal,...
• Load a different 8-bit \mathcal alphabet with mathalpha
• Manually adjust the kerning with \mkern commands (see answer by Henri Menke).

Edit by correct comment of the user @ Henri Menke.

\documentclass[12pt]{article}
\usepackage{mathtools}

\begin{document}
\begin{equation*}
dx_{\mathcal{AB}}^{\mu} + dx_{\mathcal{BC}}^{\mu} + dx_{\mathcal{C\mkern-1mu D}}^{\mu} + dx_{\mathcal{D\mkern-2mu A}}^{\mu} \ne 0.
\end{equation*}

\end{document}


• You should use \mkern instead of \hspace, e.g. \mathcal{C\mkern-1mu D} and \mathcal{D\mkern-2mu A}. And of course you should remove all the document options and packages that are not actually needed for this example, which is all of them in this case. Jul 14 '20 at 2:10
• @HenriMenke Hi, and excuse me again. I have forgotten that in math mode I must use \mkern. Thank you very much for your comment that I have appreciated. Jul 15 '20 at 23:27