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Koszul resolution for a rank-two free abelian group
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Mathematics
Area of mathematics
Algebra
Group theory
Group cohomology
Projective-resolution definition of group cohomology
2026-09-28
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For
G
=
⟨
x
,
y
∣
x
y
=
y
x
⟩
, the trivial
Z
G
-module has the
free resolution
0
⟶
Z
G
(
x
−
1
1
−
y
)
(
Z
G
)
2
(
x
−
1
y
−
1
)
Z
G
⟶
Z
⟶
0.
(1)
Table of contents
Second cohomology of a rank-two free abelian group with truncated group-ring coefficients
Koszul resolution for a rank-two free abelian group
Second cohomology of a rank-two free abelian group with truncated group-ring coefficients
0
0
0
Koszul resolution for a rank-two free abelian group
If
G
≅
Z
2
,
I
is the
augmentation ideal
, and
M
=
Z
G
/
I
2
, then
H
2
(
G
,
M
)
≅
M
/
I
M
≅
Z
.
(1)
The
quotient map
M
→
Z
G
/
I
≅
Z
induces an
isomorphism
in
second
cohomology
.
Ancestors
(7)
Projective-resolution definition of group cohomology
Group cohomology
Group theory
Algebra
Area of mathematics
Mathematics
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(1)
Past exam of the mathematics course of the University of Cambridge
/
2023
/
iii
/
Paper 151
/
1
/
Solution
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