binary/unary operator in TeX-like math mode

[Omikhleia]

SILE 0.14.5

Using the regular minus dash (-) or the minus unicode symbol U+2212 (−) in TeX-like math:

\begin{document}
\use[module=packages.math]

\math[mode=display]{\pi=\sum_{k=0}^\infty\frac{1}{16^k}(\frac{4}{8k+1} - \frac{2}{8k+4} - \frac{1}{8k+5} - \frac{1}{8k+6})}

\math[mode=display]{\pi=\sum_{k=0}^\infty\frac{1}{16^k}(\frac{4}{8k+1} − \frac{2}{8k+4} − \frac{1}{8k+5} − \frac{1}{8k+6})}

\math[mode=display]{e^{i\pi} = -1}

\math[mode=display]{e^{i\pi} = −1}

\end{document}

Both cases apparently use U+2212 for the rendering of the formula (which seems great).

However:

• In the case U+2212 is used, it is better-looking as a binary operator, but badly looking as a unary operator.
• Inversely for the regular minus (which, theoretically at least, is probably the only valid option in TeX), looking better as unary operator, but being too close to the content as binary operator.

More generally perhaps, both \pm and + work well as binary operators, but are not so nicely placed as unary operator.

Experimenting with online renderers to MathJax and LaTeX, all cases with regular -, + or \pm look consistent with my expectations, so perhaps there would be a way to better handle unary vs. binary use of such operators in SILE's math implementation?