Does anyone have any idea what this character is for: ⋳
"element of with vertical bar at end of horizontal stroke (U+22F3)"

Very grateful to be invited to write this book review for the Notices! It was a fun opportunity to explore the wide range of logic puzzles and games that exist in the world, and how they intersect with mathematics. Check it out at

If you like logic puzzles, has some fun logic at 4km and 5km today.

Opinions please!

I'm the lead developer for an open-source project, Numbas (

We have a mailing list on google groups for support and discussion, but I'd like something (1) not hosted by google, and (2) a bit more real-time.

It should have archives visible to the public, and ideally be indexed by search engines.

Zulip seems ideal, but public channels aren't search indexed. Other options ticking fewer boxes are Discord, Discourse, or Matrix.

Any other suggestions?

To solve this puzzle: Mario can jump on a radius of four Goombas, or strike a 2×2 square on the inner two rows. You have two moves.

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Still obsessed about how Nintendo made Abstract Algebra the video game and I'm just now playing it. Each battle takes an optimal configuration of enemies, applies the composition of two allowed permutations (ring/diameter cycles), and presents results to the player. Apply the right inverses in the right order and you'll one hit KO everyone before they can strike back.

Okay yeah the next time I teach intro to proofs I need some quizzes reinforcing structural stuff. Like to prove "If P(A,Z) then Z⊆A." directly one probably needs to write "Assume P(A,Z). Let x∈Z. [...] Thus x∈A, and therefore Z⊆A."

I know I'm old because I honestly can't remember if I had friends in grad school who actually applied Newton's Law of Cooling to predict the time their Thanksgiving turkey would come to temperature, or if it's just an anecdote I read on the Internet (it's something these folks would have done though).


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