MHB Each exact sequence can be arised by short exact sequences

mathmari
Gold Member
MHB
Messages
4,984
Reaction score
7
Hey! :o

Let $R$ be a commutative ring with unit.

We have that if the sequences $0\rightarrow A\rightarrow B\overset{f}{\rightarrow}C\rightarrow 0$ and $0\rightarrow C\overset{g}{\rightarrow}D\rightarrow E\rightarrow 0$ are exact, then the sequence $0\rightarrow B\overset{gf}{\rightarrow} D\rightarrow E\rightarrow 0$ is exact.

So, each exact sequence can be arised by short exact sequences as above, right? (Wondering)

But how could we prove this? Could you give me a hint? (Wondering)
 
Physics news on Phys.org
Do we show that maybe using induction on the length of a sequence?

Base case: We consider the sequence $0\rightarrow A\rightarrow B\rightarrow 0$. This is exact.

Inductive hypothesis: We assume that each exact sequnez of length $n$ is made by short exact sequences.

Inductive step: We consider a sequence of length $n+1$. The first $n$ are made by short exact sequences, because of the inductive hypothesis, right? How could we continue? (Wondering)
 
See exercise 2.6 on p.65 of Rotman - An Introduction to Homological Algebra 2nd edition 2009.
 

Similar threads

Replies
5
Views
2K
Replies
2
Views
3K
Replies
18
Views
2K
Replies
5
Views
992
Replies
15
Views
2K
Replies
1
Views
1K
Replies
7
Views
2K
Back
Top