When I was a first-year graduate student in an economics Ph.D. program, I was taking a class we called Math Econ (taught by Dr. Omar Al-Ubaydli, at the time). I also was lucky to be renting a house along with several other women in the same program. For a few weeks, our group study sessions featured epsilon and delta.
Like many aspiring economists, I had taken Real Analysis at my undergraduate institution to bulk up on math skill and impress the admissions committee.*
I never had a chance to join a sorority as an undergraduate student. It does look fun to walk around wearing a Greek code that is only fully understood by other members of a club. So, in grad school, I wanted to make shirts for what I called our “epsilon delta sorority”. We had Greek letters and a sisterhood (brotherhood). There are lots of women and men who are in the epsilon delta sorority.
It only took a decade for me to realize my dream. I have created shirts and shipped them to the girls I lived with. So more people can join, I created a store: https://shop.spreadshirt.com/economist-writing-every-day/
Here’s me wearing a t-shirt for women

Here’s a version for men

We have accessories, too. Why not? Life is too short to not put this on a mug. Someone already told me they want to give this to their daughter, so I added kids’ sizes.
I pulled out an old paper from my Math Econ course binder for this post. Here is something I had written for the class:

*If you are looking for an introduction, try Khan Academy. Taking Real Analysis before you get to an economics Ph.D. program is helpful, although not always necessary. Multivariable calculus is more practical than Real Analysis and used on a more routine basis for economists. Some subfields require more formal proofs than others.