Euler's Identity Coffee Cozy

I've been meaning to design a new coffee cozy for a while now. I've had ideas, but never actually tried anything out.

Well, that's changed. I recently drew up a sketch and embroidered a new cozy design. It's Euler's Identity, surrounded by some swirly border.

I think next time I stitch it up, I'll try using a stem stitch instead of a back stitch.