There is an abbreviation, very common in English, which stands for a French phrase that is no longer used by French speakers; an equivalent in modern French might be Merci de confirmer ta présence. What abbreviation/phrase am I thinking of?
The works of the sculptor Alexander Calder have been classified into two types, one of which is called a stabile (pronounced STAY-beel). Which four of the works above are stabiles, which one is the other type, and which one is a hybrid?
Solution
The other type is more famous! Sculpture E is a mobile. You might know mobiles as decorations for a child's nursery, but the term was coined (by fellow artist Marcel Duchamp) specifically for Calder's moving sculptures. Yet another artist, Jean Arp, sarcastically proposed that Calder's non-moving sculptures should be called stabiles, and Calder was like, sounds good. Sculptures A, B, D, and F are stabiles. Sculpture C, "Five Rudders", has aspects of both types of sculpture.
Congratulations to yesterday's solvers Nicholas, Max, Yildiz, Inca, Maddy, Jacob C., Peters M. and V., Annas J. and K., Atticus, Bridget, Jessica, Kate, SG Zach, Mr. Gregg, and Dr. Yetman. Thanks to everybody who made a guess!
Though he now teaches mathematics, Dr. (né Mr.) Shapiro's first job in a K–12 school was as a lunch monitor in Davis, CA. It was there that he originated the Puzzle of the Day, even rewarding correct answers with tickets in denominations like "15 points" (though without a clear idea of how he'd ultimately redeem these). Dr. Shapiro's favorite puzzle from this pre-professional era was "Tell me the location of the beehive on this campus."
Ten years later, Dr. Shapiro revived Puzzle of the Day at Proof School, writing each day's puzzle on a name tag. After 600 puzzles or so, he was just starting to feel normal about students reading his chest all the time when campus closed and the puzzle, like the rest of our lives, moved online. New puzzles are posted daily on school days.
Want to catch up on old PotDs? There's an archive currently containing puzzles from March 2020 to March 2021.