Why can't I use 𝔽?

Question

I can't figure out why LaTeX won't let me use the 𝔽 symbol (U+1D53D, mathematical double-stuck capital F). When I try, I get the error Package inputenc Error: Unicode char \u8:𝔽 not set up for use with LaTeX.

The input file is UTF-8 encoded. Here is a minimal working (or rather, non-working) example to demonstrate the issue.

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{mathtools}
\begin{document}
% \newcommand{\eff}[1]{F\text{#1}}
\newcommand{\eff}[1]{𝔽\text{#1}}
$ \eff{some} $
\end{document}

When using the first variant of \eff, everything works (the output is rendered as "Fsome" with an italic F, just as expected). However, if I comment that one out and instead uncomment the second variant, I get the error on line 8 (where I actually use the freshly defined command).

I'm using pdfLaTeX 3.1415926-1.40.10-2.2 from and on Debian Squeeze (package texlive-latex-base version 2009-11+squeeze1) with no special options at all (just pdflatex mwe.tex) to try to render the document.

I find it hard to believe that nobody would have wanted to use this particular symbol in a LaTeX document, so surely it can be done. What am I missing?

Answer 1

As explained at LaTeX Matters you can use the package amssymb or amsfonts together with the macro \mathbb and F as an argument. Note that you have to use \mathbb in math mode.

\documentclass{article}

\usepackage{amssymb}            % or \usepackage{amsfonts}

\begin{document}

\(\mathbb{F}\)

\end{document}

If you want to define your own macro like you do in your example this is possible with \mathbb{F} too.

Answer 2

If you want to use 𝔽 inside your document you can use:

Edit:

As egreg pointed out you can use the package newunicodechar which makes it easier:

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{amsmath,amssymb}
\usepackage{newunicodechar}
\newunicodechar{𝔽}{\ensuremath{\mathbb{F}}}
\begin{document}
𝔽
\end{document}

Original:

% !TEX program = pdflatex
\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{amsmath,amssymb}

\expandafter\def\csname u8:\detokenize{𝔽}\endcsname{\ensuremath{\mathbb{F}}}
\begin{document}
𝔽
\end{document}

The command \ensuremath is testing whether you are in math mode or not and sets the argument in math mode.

Frank Mittelbach wrote a great explanation about inputenc:

How can I get utf8 character