It's My Turn (1980) Snake Lemma
Why Mathematics Stack Exchange recommends it
Mathematics Stack Exchange users link it, often half-jokingly, as a memorable on-screen walk through the snake lemma and its connecting homomorphism when answering questions about exact sequences.
Recommended by 4 people across 4 different months, 2014 to 2024.
What it is
A 1m47s clip from the 1980 film It's My Turn, uploaded by philsproof, in which Jill Clayburgh's character, a math professor, works through a proof of the snake lemma at a blackboard. It is a short scene from a feature film, not a lecture, and the surrounding dialogue is fictional.
Cited in 2 Wikipedia articles, including Benedict Gross, Snake lemma.
What people said
Recommends tomasz · 2014-01 · Mathematics Stack Exchange · on “"Bad" Mathematics in Movies”
It's My Turn has a pretty good explanation of the snake lemma... followed by hilariously stupid discussion. It's like their consultant just up and left halfway through the scene. Or just trolled the hell out of them. [this video]
Recommends Zavosh · 2014-10 · Mathematics Stack Exchange · on “a problem in exact sequence”
The kernels go in a row above the diagram, and the cokernels go in the row below. The trickiest part of the exact sequence you need is in the middle. To construct the map $d$ one must watch this video: [this video]
Recommends wonderich · 2018-09 · Mathematics Stack Exchange · on “Long exact sequence of cohomology group "without" Snake lemma”
Let a short exact sequence $$ 0 \to L \to M \to N \to 0 $$ is a short exact sequence of $G$-modules, then a long exact sequence is induced: $$ 0\longrightarrow L^G \longrightarrow M^G \longrightarrow N^G \overset{\delta^0}{\longrightarrow} H^1(G,L) \longrightarrow H^1(G,M) \longrightarrow H^1(G,N) \overset{\delta^1}{\longrightarrow} H^2(G,L)\longrightarrow \cdot $$ The connecting homomorphism is, $$ \delta^n : H^n (G,N) \to H^{n+1}(G, L) $$ Question 1 : How to prove the above long exact sequence is true? Is this simply based on the Snake Lemma [It's My Turn (1980)] [this video] ? Or is there other simpler way to think about it, without using the Snake Lemma?
Recommends tkf · 2021-07 · Mathematics Stack Exchange · on “Morphism extends iff image trought connecting map is zero”
Elements of Ext are by definition cohomology classes in the cochain complex of maps from an injective resolution to a coefficient module (see for example [LINK] ). Starting with $f'$ we obtain an element of $Ext_R^0(M',N)$ by composing with $\iota$. Now follow the snake (as depicted in this film: [this video] ).