Question: I am trying to get a double tilde symbol over a letter but I can't find a well suiting solution. I tried

```
$\tilde{\tilde{z}}$

```

and

```
$\overset{\approx}{z}$ 

```

but both solution look a bit off.
I am trying to find something with less vertical space between the two tildes but a similar size like `\tilde{}`.

*edit:* vertical spacing

Answer: 
One of these?

```
\documentclass[12pt]{article}
\usepackage[utf8]{inputenc}
\usepackage{amsmath}
\usepackage{calc}

\usepackage{accents}
\newcommand{\dbtilde}[1]{\accentset{\approx}{#1}}
\newcommand{\vardbtilde}[1]{\tilde{\raisebox{0pt}[0.85\height]{$\tilde{#1}$}}}

\begin{document}

    \[ \vardbtilde{z}\quad \dbtilde{z} \]%

\end{document} 

```

[![enter image description here](https://i.stack.imgur.com/0wHG7.png)](https://i.stack.imgur.com/0wHG7.png)
The `tipa` package has `\doubletilde`. However, it is not made for math mode, so you have to cheat a bit:

```
\documentclass{article}
\usepackage{amsmath}
\usepackage[extra]{tipa}

\begin{document}

$\doubletilde{\kern-1pt$z$}$

\end{document}

```

[![enter image description here](https://i.stack.imgur.com/yt222.png)](https://i.stack.imgur.com/yt222.png)