Minion pro spacing

Question

I recently managed to install the package minionpro (I use pdfLatex). It seems to me that the spacing is sometimes off, for example:

$$\square p \to  \square \square p$$
$$ P(a|b) = \frac{P(b|a)P(a)}{P(b)} $$

gives the following, where there is more space than necessary (between the two squares, between the square and 'p', before 'a' and after 'b' in P(a|b)...)

I made the fonts following the procedure in the minionpro package readme (and not using fontpro), I wonder if that makes a difference.

MWE:

\documentclass{article}

\usepackage{MinionPro}
\begin{document}
$$\square p \to  \square \square p$$
$$ P(a|b) = \frac{P(b|a)P(a)}{P(b)} $$
\end{document}

Answer 1

The “inconsistent” spacing around \square arises because \square is a binary operator (you will find the same behaviour with any other font and any other binary operator, e.g. +p \to ++p). To overcome this, you have to wrap the consecutive squares into the \mathbin primitive to keep the overall binary class of the operator. If you use it more than once in your document it is useful to define a command for it.

The second problem with the spacing around (a|b) cannot be fixed from the macro level. You'd have to patch the virtual fonts with additional kerning pairs.

\documentclass{article}
\usepackage{MinionPro}
\newcommand*\dblsquare{\mathbin{\square\square}}
\begin{document}
\[ \square p \to \dblsquare p \]
\[ P(a|b) = \frac{P(b|a)P(a)}{P(b)} \]
\end{document}

---

There also exists a proper math companion font for Minion Pro called Minion Math which does not have these problems because it has been carefully designed and is an actual math font. However, it is a commercial font and it's not cheap: http://typoma.de/en/fonts.html#mnm_pricing

\documentclass{article}
\usepackage[onlytext]{MinionPro}
\usepackage{minionmath}
\newcommand*\dblsquare{\mathbin{\square\square}}
\begin{document}
\[ \square p \to \dblsquare p \]
\[ P(a|b) = \frac{P(b|a)P(a)}{P(b)} \]
\end{document}