Graduate School: A form of bipolar disorder?

Imaginary Friends

Being married to a mathematician exposes me to a lot of field-specific humor that I don’t always understand. A lot of the times, I just have to nod and smile. But this is a math joke that I actually get, and though I had to dig deep into the recesses of my math knowledge to laugh at it, I think it’s very cute:

Speculations on Year 8?