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I know versions of this question have already been asked, but I've already spent a couple of hours trying to make their answers work in my case, and wasn't able to.

I would like a dedicated symbol to use for Kronecker deltas, which doesn't get confused with other deltas in my document. For this I would like to import the delta from one of the fonts in this list, say the one on page 9. I only want to import one character, and would like a new command for it that does not overwrite the ordinary \delta. What is the quickest way to achieve this?

Thank you.

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The solution will be different depending on whether you use unicode-math or legacy 7-bit math fonts. Here is a solution that uses unicode-math if the engine supports it, and otherwise falls back to the font you specified:

\documentclass{article}
\usepackage{iftex} % For /iftutex
\usepackage[paperwidth=10cm]{geometry} % To format this MWE for TeX.SX
\pagestyle{empty}

\iftutex
  % LuaTeX or XeTeX
  \usepackage{unicode-math}
  \setmathfontface\altgrfont{AntykwaTorunskaMed-Italic.otf}[Scale=MatchLowercase]
  \newcommand{\kronecker}{\altgrfont{δ}}
\else
  % PDFTeX
  \usepackage[T1]{fontenc}
  \usepackage[utf8]{inputenc} % The default since 2018
  \usepackage{amsmath}
  \DeclareSymbolFont{altgr}{OML}{antt}{m}{it}
  \DeclareMathSymbol{\kronecker}{\mathord}{altgr}{"0E}
\fi

\begin{document}
\begin{tabular}{c c c}
  Kronecker delta & \texttt{{\textbackslash}delta} & \texttt{{\textbackslash}partial} \\
  \(\kronecker\)  & \(\delta\)                 & \(\partial\)
\end{tabular}
\end{document}

antt font sample

In PDFTeX, you can change the family name to get another font, or even change OML to LGR to use a LGR-encoded font. if you don’t want to waste one of your limited number of math alphabets on this one symbol, you could instead switch to \textnormal and generate it with text-mode commands, e.g. \usefont followed by \symbol.

You would need one extra line of code in each case to declare a bold version, which you might for example use in a bold header.

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  • Perfect, thanks so much. – Emilio Ferrucci Jul 25 '20 at 15:26
  • Great....answer. – Sebastiano Jul 25 '20 at 17:44
  • Not sure why you suggest Artemisia, when Antikwa Toruńska is also available as an OpenType font in TeX Live: /usr/local/texlive/2020/texmf-dist/fonts/opentype/public/antt/ – egreg Jul 25 '20 at 20:21
  • @egreg I’d used it before in other answers, because a question years ago requested it. But, producing the same output on all engines would probably have been better here. – Davislor Jul 25 '20 at 20:45

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