# Changing symbol size when used as subscript

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?

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}


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.

• 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