Music theory (after a long break)

The first evening of the choir, this year. We changed the choir from a pure singing activity into a course at the local community college (Folk high school). Now we sing but we also learn a bit about how music and notes work. Here we were learning about the bass and treble clef, how they relate, and where the symbols come from.
I started learning this as a 7 year-old during a short period of violin lessons and here I am continuing my education. I must say it is much more interesting now than it was 55 years ago.