Is there a font where lower-case $x$ and $z$ look more like $X$ and $Z$, and how do I switch all my equations to have that font?

Question

I like $X$ and $Z$ more than $x$ and $z$. The lower case versions are too fancy (too many curves, whereas the $X$ and $X$ have lines that are more "straight"). Is there a font where the lower case $x$ and $z$ are just smaller versions of the straight-line containing $X$ and $Z$? How do I change my LaTeX preamble so that all math mode occurrences of $x$ and $z$ use that font, but the rest of the alphabet remains the same?

For example, \mathrm{x} and \mathrm{z} look fine to me. Is there a way to make all occurrences of x and z in math-mode, to look like \mathrm{x} and \mathrm{z}, while allowing the rest of the alphabet to be unaffected?

Answer 1

The default fonts are defined in fontmath.ltx.

The relevant lines for x and z are:

\DeclareSymbolFont{letters}     {OML}{cmm} {m}{it}
\DeclareMathSymbol{x}{\mathalpha}{letters}{`x}
\DeclareMathSymbol{z}{\mathalpha}{letters}{`z}

So x and z will be set in cmmi. We could instead use the slanted variant of cmr just for these characters:

\DeclareSymbolFont{lettersslanted}{OT1}{cmr}{m}{sl}
\DeclareMathSymbol{x}{\mathalpha}{lettersslanted}{`x}
\DeclareMathSymbol{z}{\mathalpha}{lettersslanted}{`z}

MWE

\documentclass{article}
\DeclareSymbolFont{lettersslanted}{OT1}{cmr}{m}{sl}
\DeclareMathSymbol{x}{\mathalpha}{lettersslanted}{`x}
\DeclareMathSymbol{z}{\mathalpha}{lettersslanted}{`z}
\begin{document}
$xyz$

$XYZ$
\end{document}