Michael Kinyon
@profkinyon.bsky.social
Mathematics professor at the University of Denver. Quasigroups, Semigroups, Automated Deduction. He/Him. Occasionally drop in at Mathstodon, but not as much as I used to.
skircle versus skycle
October 5, 2025 at 4:58 PM
skircle versus skycle
One of these things is not like the others, WolframAlpha
September 8, 2025 at 3:18 PM
One of these things is not like the others, WolframAlpha
I just hope it's also injectivtive so then it would be bijectivtive.
(I probably made this typo, but I'm still going to blame my coauthor.)
(I probably made this typo, but I'm still going to blame my coauthor.)
![Hence $\phi$ is surjectivtive [sic]](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:pdqysfi2zlmipxpbxsdnw433/bafkreicdwbyctekikkzshtvfxbhdcpjs3i6tqqxv66wcxr43oyzudykzxm@jpeg)
June 21, 2025 at 3:58 PM
I just hope it's also injectivtive so then it would be bijectivtive.
(I probably made this typo, but I'm still going to blame my coauthor.)
(I probably made this typo, but I'm still going to blame my coauthor.)
It's also fun to discuss nonconvex quadrilaterals. Showing them to students and pointing out that they still satisfy the definition of quadrilateral can be mind opening for them. We had an especially good discussion of how one precisely defines "convex".
June 9, 2025 at 11:39 PM
It's also fun to discuss nonconvex quadrilaterals. Showing them to students and pointing out that they still satisfy the definition of quadrilateral can be mind opening for them. We had an especially good discussion of how one precisely defines "convex".
If you're the type of mathematics teacher who likes to give exercises requiring exact values of trig functions, but is bored with the old 30°-45°-60° grind, then the Ailles rectangle may be for you!
(Seriously, this thing is why I can write down sin(15°), cos(75°) etc without using identities.)
(Seriously, this thing is why I can write down sin(15°), cos(75°) etc without using identities.)
June 4, 2025 at 8:14 PM
If you're the type of mathematics teacher who likes to give exercises requiring exact values of trig functions, but is bored with the old 30°-45°-60° grind, then the Ailles rectangle may be for you!
(Seriously, this thing is why I can write down sin(15°), cos(75°) etc without using identities.)
(Seriously, this thing is why I can write down sin(15°), cos(75°) etc without using identities.)
One reason my back often hurts is that someone won't allow me to push my chair closer to my desk
May 31, 2025 at 1:01 AM
One reason my back often hurts is that someone won't allow me to push my chair closer to my desk
My students have accused me of having boring title slides so here is what I am using today.
May 29, 2025 at 4:39 PM
My students have accused me of having boring title slides so here is what I am using today.
"If you like, it is magic."
May 27, 2025 at 6:43 PM
"If you like, it is magic."
We are visiting eastern Utah for the long weekend. This is the Great Hunt, a petroglyph located in Nine Mile Canyon. It is believed to have been created by the Fremont people (ca 950-1200 CE). The depicted animals are bighorn sheep, probably during the fall mating season.
May 25, 2025 at 12:13 AM
We are visiting eastern Utah for the long weekend. This is the Great Hunt, a petroglyph located in Nine Mile Canyon. It is believed to have been created by the Fremont people (ca 950-1200 CE). The depicted animals are bighorn sheep, probably during the fall mating season.
Remember that if you want to stretch terminology in a mathematics book or paper, you are allowed to do so if you announce your intentions in French.
![Definition. With the above notation acute angles XPQ and X'PQ are called *angles of parallelism* for segment PQ. Lobachevsky denoted their congruence class [or, par abus de langage, any angle congruent to them] by Pi(PQ).
(I have underlined the French phrase in red.)
From M.J. Greenberg, _Euclidean and non-Euclidean geometries: development and history_, 4th ed., W.J. Freeman, 2008, p. 260](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:pdqysfi2zlmipxpbxsdnw433/bafkreihp4rylxnvfs5j65nffzmcadp5uocztw5b6s2a463epwuiuxjnpvi@jpeg)
May 22, 2025 at 4:44 PM
Remember that if you want to stretch terminology in a mathematics book or paper, you are allowed to do so if you announce your intentions in French.
How I write positive referee reports
April 16, 2025 at 10:48 PM
How I write positive referee reports
Reskeet with an image of your favorite James Bond (wrong answers only)
April 13, 2025 at 3:12 AM
Reskeet with an image of your favorite James Bond (wrong answers only)
A rug in the shape of an Australian shepherd
April 6, 2025 at 3:32 AM
A rug in the shape of an Australian shepherd
An excerpt of a handout I use in my geometry class. The more engaged students seem to like thinking about this sort of thing.
April 1, 2025 at 5:28 PM
An excerpt of a handout I use in my geometry class. The more engaged students seem to like thinking about this sort of thing.
I hope my students appreciate the FromSoft-style fog gate I'm going to set up in the doorway to the classroom before they take their final exam.
March 20, 2025 at 12:49 AM
I hope my students appreciate the FromSoft-style fog gate I'm going to set up in the doorway to the classroom before they take their final exam.
Post your favorite Doctor Who, wrong answers only.
March 19, 2025 at 3:13 PM
Post your favorite Doctor Who, wrong answers only.
One of the better prefaces I have read.
(Source in the alt text)
(Source in the alt text)
March 18, 2025 at 5:01 PM
One of the better prefaces I have read.
(Source in the alt text)
(Source in the alt text)
Here is the table of contents. In addition to the linear algebra content, do you notice anything else unusual compared to today's textbooks? (Answer is in the alt text.)
March 13, 2025 at 3:52 PM
Here is the table of contents. In addition to the linear algebra content, do you notice anything else unusual compared to today's textbooks? (Answer is in the alt text.)
This is a delightful little book. It was published in 1959 and as you can see, it cost a whopping $1.25.
March 13, 2025 at 3:48 PM
This is a delightful little book. It was published in 1959 and as you can see, it cost a whopping $1.25.
I like to think of those identities that way. It's the "wrapping" homomorphism from to R to SO(2) (or written as complex numbers instead of matrices, from R to S^1 = SU(1) ).
March 12, 2025 at 9:54 PM
I like to think of those identities that way. It's the "wrapping" homomorphism from to R to SO(2) (or written as complex numbers instead of matrices, from R to S^1 = SU(1) ).
Giving my students a reasonable warning
March 9, 2025 at 8:44 PM
Giving my students a reasonable warning
I love this visualization.
March 7, 2025 at 7:10 PM
I love this visualization.
As fall quarter winds down, we are slowly moving into review mode in my calculus class. I'm going to ask them about this well known "paradox" and see how many of them can figure out where things go wrong.
March 6, 2025 at 4:33 PM
As fall quarter winds down, we are slowly moving into review mode in my calculus class. I'm going to ask them about this well known "paradox" and see how many of them can figure out where things go wrong.