curl

Today I come across a command line tool known as cURL that can retrieve stuff from a URL.
This reminded of the "inverted triangle" operator. See glorious details here.

There is a very good (classic) book named Div, Grad, Curl and all that that helped me understand some of that stuff.
This book has helped students for decades.

The curl appears in the differential form of the glorious Maxwell Equations that governs electromagnectic forces. I want to buy a T-shirt with these 4 beautiful equations on them.