On 12 Jul 2012, at 21:03, Jukka K. Korpela wrote: > 2012-07-12 21:07, Asmus Freytag wrote: > >> What the examples show from TeX is that colon and ratio cannot be >> substituted for each other without affecting the display. > > This looks like a problem in TeX rather than character standards. If TeX can > space $a+b$ properly, what’s the issue with $a:b$? And when I tested it, I > got proper spacing, corresponding to the example in “Detailtypographie” > (which mentions that the colon, Doppelpunkt, is used “eventuell aus > didaktischen Gründen, sonst eher veraltet oder als »verhält sic zu« > verwendet”). > > However, it might be argued that disambiguation is desirable, because COLON > is also used as punctuation symbol in mathematical expressions, as in “f: A → > B” and here (arguably) there should be some spacing after the colon but not > before it.
In original TeX, there should be $a:b$ and $f\colon A \rightarrow B$. If you want to use Unicode characters, it is possible with (compiled with lualatex): \documentclass{article} \usepackage{amsmath} \usepackage{fontspec} \usepackage[math-style=literal,colon=literal]{unicode-math} \defaultfontfeatures{Ligatures=TeX} \setmainfont{XITS} \setmathfont{XITS Math} \begin{document} $f: A → 𝑩, 𝐁, B, 𝗕, 𝘽$ and $a∶b$. \end{document} Here, colon=literal causes the two colon types behave as marked in Unicode, and math-style=literal causes the same for the mathematical semantic styles. Hans