The symbol looks like this:
In context:
It occurs in the paper: "Linear type theory for asynchronous session types - S. J. Gay & V. T. Vasconcelos".
What command can I use to generate this symbol? I've tried \overset{\smile}{\frown} but it doesn't look quite right - the \frown comes out too big.
$\asymp$withamsmath. Use http://detexify.kirelabs.org/classify.html – Steven B. Segletes Sep 18 '17 at 10:49