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divbyzero.bsky.social
Dave Richeson
@divbyzero.bsky.social
1.8K followers 490 following 11K posts
Mathematician. John J. & Ann Curley Chair in Liberal Arts at Dickinson College. Author of Tales of Impossibility and Euler's Gem. Coffee drinker. [Everything in the timeline before October 2024 was imported from my Twitter/X feed 2008-24.]
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divbyzero.bsky.social
Dave Richeson @divbyzero.bsky.social · Oct 21
Since I'm new here, I'll introduce myself. I'm a math prof at Dickinson College. I'm author of Euler's Gem and Tales of Impossibility. I was editor of Math Horizons. I am interested in topology, dynamical systems, geometry, history of math, recreational math, math & art, and expository math writing.
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divbyzero.bsky.social
Dave Richeson @divbyzero.bsky.social · 1d
Check out the online silent auction fundraiser for Gathering 4 Gardner @gathering4gardner.bsky.social! It features puzzles, books, and even the original notebooks from Vi Hart's videos. Check it out and place some bids! The link is at the bottom of this page: www.gathering4gardner.org/auction2025/
G4G 2025 Fall Benefit Auction
VIEW EBAY ITEMS (starting Oct 11) The G4G 2025 Fall Online Benefit Auction is taking place October 11 – 18, 2025.  Now is the perfect time to get gifts for the holidays, birthdays, a…
www.gathering4gardner.org
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divbyzero.bsky.social
Dave Richeson @divbyzero.bsky.social · 1d
In the "kids are cute" category. This was my Facebook memory from 15 years ago:

"I like that [daughter who's now in college]'s new doll is named Alison, as in ‘Alison Wonderland.’”
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divbyzero.bsky.social
Dave Richeson @divbyzero.bsky.social · 2d
12:45 AM EDT. MESSAGE FROM WTSP/TV."

See: en.wikipedia.org/wiki/Specifi...
Specific Area Message Encoding - Wikipedia
en.wikipedia.org
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divbyzero.bsky.social
Dave Richeson @divbyzero.bsky.social · 2d
annoying sound. It is an encrypted message sent three times. This sample message encodes "A REQUIRED WEEKLY TEST HAS BEEN ISSUED FOR THE FOLLOWING COUNTIES/AREAS: HILLSBOROUGH FL, MANATEE FL, PASCO FL, PINELLAS FL, AND SARASOTA FL AT 12:15 AM EDT ON OCTOBER 5, 2005 EFFECTIVE UNTIL
Specific Area Message Encoding - Wikipedia
en.wikipedia.org
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divbyzero.bsky.social
Dave Richeson @divbyzero.bsky.social · 2d
My son's home for fall break. He loves to share random things he's come across. Today, he told me about SAME (Specific Area Message Encoding). This is the bzzt-bzzt-bzzt sound that precedes an emergency alert. Listen to tis sample: en.wikipedia.org/wiki/File:Sa... It is not a random burst of
en.wikipedia.org
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divbyzero.bsky.social
Dave Richeson @divbyzero.bsky.social · 3d
Same
divbyzero.bsky.social
Dave Richeson @divbyzero.bsky.social · 4d
I used this on a take-home exam during COVID. Then I used a modified version (with two quantifies) on an exam this semester. It’s fun!
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divbyzero.bsky.social
Dave Richeson @divbyzero.bsky.social · 4d
The response took 27 seconds. (Source: www.infinitelymore.xyz/p/monkey-mad...)
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divbyzero.bsky.social
Dave Richeson @divbyzero.bsky.social · 4d
I was curious if ChatGPT 5 could solve this entertaining logic problem (created by @joeldavidhamkins.bsky.social). I shared the screenshot below and gave it the prompt "Solve the following logic problem." It requires figuring out the logic and matching it to a "scene." Its response in the next post.
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divbyzero.bsky.social
Dave Richeson @divbyzero.bsky.social · 4d
There's a nice article by Siobhan Roberts about the Bridges 2025 conference in Eindhoven in the NY Times. I can now say that I am in The NY Times! (A photo credit for the shot of Chaim Goodman-Strauss and Edmund Harriss,... but still!) www.nytimes.com/2025/10/10/s...
Every Artist Has a Favorite Subject. For Some, That’s Math.
www.nytimes.com
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divbyzero.bsky.social
Dave Richeson @divbyzero.bsky.social · 5d
Very nice! If you follow the link to Want and Zhang's preprint, here's the figures they gave.
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Reposted by Dave Richeson
divbyzero.bsky.social
Dave Richeson @divbyzero.bsky.social · 6d
New blog post! Through a sequence of images, I verify that the unknotting number of the connected sum of a (2,7) torus knot and its mirror is less than 6: I show that this first image is the connected sum, and after changing those crossings, it produces the unknot! divisbyzero.com/2025/10/08/t...
A drawing of the connected sum of a (2,7) torus knot and its mirror image (much modified). An image of a crazy knot I claim is the unknot.
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divbyzero.bsky.social
Dave Richeson @divbyzero.bsky.social · 5d
That works! I thought of it as flipping over the bottom knot and then running the string around the top one.
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Dave Richeson @divbyzero.bsky.social · 6d
Fact: this took me a week. I kept coming back to it, fixing mistake after mistake after mistake!
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divbyzero.bsky.social
Dave Richeson @divbyzero.bsky.social · 6d
New blog post! Through a sequence of images, I verify that the unknotting number of the connected sum of a (2,7) torus knot and its mirror is less than 6: I show that this first image is the connected sum, and after changing those crossings, it produces the unknot! divisbyzero.com/2025/10/08/t...
A drawing of the connected sum of a (2,7) torus knot and its mirror image (much modified). An image of a crazy knot I claim is the unknot.
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divbyzero.bsky.social
Dave Richeson @divbyzero.bsky.social · 15d
That's nice. Thanks! Goodness knows, they've seen me make typos in class and on their assignments.
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Dave Richeson @divbyzero.bsky.social · 15d
There's that!! 😂
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divbyzero.bsky.social
Dave Richeson @divbyzero.bsky.social · 15d
That's definitely a good rule for everyone!
divbyzero.bsky.social
Dave Richeson @divbyzero.bsky.social · 15d
It works! Cool. THanks for the link
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divbyzero.bsky.social
Dave Richeson @divbyzero.bsky.social · 15d
the AI write it for you.
• Show respect to the person you are writing to—address them appropriately, use proper punctuation and capitalization, etc. But do not stress out about it if it is not perfect. It is just an email!
• You can always talk to me in person!

What else would you suggest?
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divbyzero.bsky.social
Dave Richeson @divbyzero.bsky.social · 15d
times when they've asked me for help writing an email or proofreading something they've written.

I'm going to tell my students:
• Write it yourself. We want to hear your voice in your email.
• You can ask AI for suggestions about what or how to write the email if you want to, but don't have
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divbyzero.bsky.social
Dave Richeson @divbyzero.bsky.social · 15d
perfectly boring and lacking in humanity. "I hope this email finds you well. Unfortunately, I am feeling under the weather..."

Having college-aged kids of my own, I know that corresponding with professors and other authority figures in writing is challenging for them. There have been countless
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divbyzero.bsky.social
Dave Richeson @divbyzero.bsky.social · 15d
I'm going to chat with my students about email.

A few years ago, we would complain that student emails read like text messages to their friends—ultra informal, all lowercase, etc. "yo prof what sections is the exam on"

Now, we've swung in the opposite direction. They are written by AI. They are
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divbyzero.bsky.social
Dave Richeson @divbyzero.bsky.social · 17d
you is wrong. The problem is, we don't know which 50%."
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Dave Richeson @divbyzero.bsky.social · 17d
Where does survey design fall on this list?

A better question: In a class about X, what percentage of info you're taught is true, correct, or will still be believed 20 years from now? Math would do pretty well.

My dad taught med school and told his students, "50% of what we will teach
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