+/* The math units. Quoting TeX by Topic, p.205:
+ *
+ * Spacing around mathematical objects is measured in mu units. A mu
+ * is 1/18th part of \fontdimen6 of the font in family 2 in the
+ * current style, the ‘quad’ value of the symbol font.
+ *
+ * A \thickmuskip (default value in plain TeX: 5mu plus 5mu) is
+ * inserted around (binary) relations, except where these are preceded
+ * or followed by other relations or punctuation, and except if they
+ * follow an open, or precede a close symbol.
+ *
+ * A \medmuskip (default value in plain TeX: 4mu plus 2mu minus 4mu)
+ * is put around binary operators.
+ *
+ * A \thinmuskip (default value in plain TeX: 3mu) follows after
+ * punctuation, and is put around inner objects, except where these
+ * are followed by a close or preceded by an open symbol, and except
+ * if the other object is a large operator or a binary relation.
+ *
+ * See the file MathClass.cpp for a formal implementation of the rules
+ * above.
+ */
+
+int mathed_mu(FontInfo const & font, double mu)
+{
+ MetricsBase mb(nullptr, font);
+ return Length(mu, Length::MU).inPixels(mb);
+}
+
+int mathed_thinmuskip(FontInfo const & font) { return mathed_mu(font, 3.0); }
+int mathed_medmuskip(FontInfo const & font) { return mathed_mu(font, 4.0); }
+int mathed_thickmuskip(FontInfo const & font) { return mathed_mu(font, 5.0); }
+