Symbol similar to \equiv

Question

What's the command for typing 3 lines exactly like \equiv but with index in the middle of top line? Thanks.

EDIT: this is the symbol I meant

Answer 1

this does not exist as a "precomposed" symbol. however, amsmath provides a mechanism for creating combinations of this sort -- \overset:

\documentclass{article}
\usepackage{amsmath}
\begin{document}
$ x \overset{0}{\equiv} y $
\end{document}

when \overset is applied to a single symbol, the proper class of that symbol (e.g., \mathrel, \mathbin) is recognized automatically, so there is no need to specify it.

of course, if the compound symbol is to be used more than once, it's a good idea to define a command to access it.