Talk:Snake lemma

Technical Questions

I don't "see" the snake in the 3rd disagram (perhaps because I'm not familiar with how the kernerls and cokernels tie in). Can someone clarify? Chas zzz brown 21:25 Oct 29, 2002 (UTC)

In the last diagram, you want to add (maybe in some other color) arrows from ker a to ker b, from ker b to ker c, from coker a to coker b and from coker b to coker c and then the connecting map from ker c to coker a in the form of a reversed S across the whole diagram. AxelBoldt 22:06 Oct 29, 2002 (UTC)

Yes, d needs to come out to the right from ker c, around the 0 on the right, left directly through the letter c, then the letter b, then the letter a around the 0 on the left, and then pop into coker a. That's the snake. — Toby 10:38 Oct 31, 2002 (UTC)

Like that? Chas zzz brown 09:28 Nov 1, 2002 (UTC)

Yes, that's a beauty. AxelBoldt 00:09 Nov 2, 2002 (UTC)

Exactly! But I don't suppose that you could label the snaky morphism "d"? Somewhere to the right of the "c" and below the nearby "0"? That would make it clearer to people comparing this to the previous diagram with its "d". — Toby 10:17 Nov 3, 2002 (UTC)

I tried it below the "0", but it was getting a bit crowded there, and it becam hard to tell visually whether d might be the 0-morphism C → 0; I think it's more readable when placed at the right as shown here. Hope you like it! Chas zzz brown 03:04 Nov 4, 2002 (UTC)

Great, thanks! — Toby 07:15 Nov 17, 2002 (UTC)

Long exact sequence

This is probably stupid, but how do you get from the Snake Lemma to the theorem that a short exact sequence of chain complexes induces the familiar long exact sequence? —Preceding unsigned comment added by 24.60.180.59 (talk • contribs) 31 May 2004

The Graduate

"The statement of the theorem could be seen written in a blackboard behind Dustin Hoffman at the very beginning of the 1967 film The Graduate."

I've wachted the whole film and I haven't seen it!

Caiodnh (talk) 11:21, 8 July 2009 (UTC)[reply]

Agreed. I couldn't find it either. —Preceding unsigned comment added by 129.74.86.30 (talk) 05:27, 11 September 2009 (UTC)[reply]

Abelian Categories

I think this page should feature a proof of the Snake Lemma in Abelian Categories without using the Embedding Theorem. Imho this is very illustrative and can be found for example in Gelfand-Manin. Is this to advanced for this page? —Preceding unsigned comment added by T3kcit (talk • contribs) 10:11, 21 March 2010 (UTC)[reply]

Since it is claimed in the first paragraph that "The snake lemma is valid in every abelian category..." the fourth paragraph entitled "Construction of the maps" should at least have some mention of the Mitchell full embedding theorem and its implicit use before diving into the construction of the connecting homomorphism d using diagram chase methods. To a novice reader unfamilar with the generality of abelian categories it would be helpful to make the distinction clear between diagram chases in general to prove theorems like this and those proofs of the same theorems that use only the slightly more abstract (co)universal properties of the objects involved in the diagrams. — Preceding unsigned comment added by 71.21.89.0 (talk) 16:47, 28 August 2015 (UTC)[reply]

Discussion elsewhere

This article is being discussed at Wikipedia talk:Scientific citation guidelines#Snake lemma as example. Tijfo098 (talk) 11:23, 28 November 2010 (UTC)[reply]

3rd isomorphism theorem

The fact that the snake lemma can be used to prove the 3rd isomorphism theorem (by the numbering in the wikipedia article 'Isomorphism Theorems') would be a nice thing to include in the article if anyone feels like doing so.