2

This is a follow-up to this question.

I'd like to define \fa to display \forall when typed as usual but be \mathsmaller{\forall} when \fa is used as a subscript. For example, I want to write sentences like

Let $(\K_\fa, \leq_\fa)$ be the $\fa$-closure of ...

and have the first \fa display in regular size but the second display using \mathsmaller.

Is there any easy way to do this?

3

You have to do nothing different from

\newcommand{\fa}{\forall}

Let's try it.

\documentclass{article}

\newcommand{\fa}{\forall}

\begin{document}

Let $(K_\fa, {\leq}_\fa)$ be the $\fa$-closure of whatever.

\end{document}

enter image description here

Note the braces around \leq when it's not used as a relation symbol, but as the name of the relation. Of course you'll continue to write

$a \leq_\fa b$

when the symbol is used in its proper sense.

You might do

\documentclass{article}

\newcommand{\fa}{{
  \mathchoice{\forall}{\forall}{\scriptscriptstyle\forall}{\forall}
}}

\begin{document}

Let $(K_\fa, {\leq}_\fa)$ be the $\fa$-closure of whatever.

\end{document}

but the result would look very dubious.

enter image description here

  • Thanks! The second one is exactly what I want. It actually looks better to me; maybe I've just been staring at these too long. I think the reason is that I often subscript \K and \leq with letters; so with this solution the symbol \forall as a subscript looks about the same size as the letter 'd' for example – jdbrody Nov 4 '15 at 21:20

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