# Christmas cracker joke III

Behind today’s door… A joke!

This post was part of the Chalkdust 2016 Advent Calendar.

## $\sqrt{\frac{-1}{64}}$

Atheeta is a PhD student at UCL in the area of mathematical ecology. He also has interests in evolutionary game theory and social dynamics.
@atheeta2    + More articles by Atheeta

• ### Book of the Year 2020

We announce the winner of this coveted prize