Decrease vertical whitespace when stacking above and below arrow

Question

I'd like to have symbols below and above an arrow. The best result so far is accomplished using

\stackrel{\tau}{\underset{\equiv}{\rightarrowtriangle}}}}

However, the vertical distance between the symbols is quite large, which also causes this construct to be quite high. How can I decrease these distances? Using \vspace seems to be wrong, as I intend to use the construct in different environments (and font sizes).

Answer 1

With stacks, you can tell it the gap separation with an optional argument.

\documentclass{article}
\usepackage{amsmath}
\usepackage{stackengine}
\stackMath
\usepackage{stmaryrd}
\begin{document}
$\stackon[1pt]{\stackunder[1pt]{\rightarrowtriangle}{\scriptstyle\equiv}}{\scriptstyle\tau}$
vs.
$\stackrel{\tau}{\underset{\equiv}{\rightarrowtriangle}}$
\end{document}