David J. Green

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Cohomology of group number 2221 of order 128

About the group

Ring generators

Ring relations

Completion information

Restriction maps

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General information on the group

• The group has 5 minimal generators and exponent 4.
• It is non-abelian.
• It has p-Rank 4.
• Its center has rank 2.
• It has 5 conjugacy classes of maximal elementary abelian subgroups, which are of rank 3, 3, 4, 4 and 4, respectively.

Structure of the cohomology ring

General information

• The cohomology ring is of dimension 4 and depth 3.
• The depth exceeds the Duflot bound, which is 2.
• The Poincaré series is

  t2  +  t  +  1

  (t  −  1)4 · (t2  +  1) · (t4  +  1)

• The a-invariants are -∞,-∞,-∞,-4,-4. They were obtained using the filter regular HSOP of the Benson test.

About the group

Ring generators

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Ring generators

The cohomology ring has 8 minimal generators of maximal degree 8:

1. b_1_0, an element of degree 1
2. b_1_1, an element of degree 1
3. b_1_2, an element of degree 1
4. b_1_3, an element of degree 1
5. b_1_4, an element of degree 1
6. c_2_13, a Duflot regular element of degree 2
7. b_5_76, an element of degree 5
8. c_8_194, a Duflot regular element of degree 8

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Ring relations

There are 6 minimal relations of maximal degree 10:

1. b_1_0·b_1_2
2. b_1_4² + b_1_1·b_1_3 + b_1_0·b_1_4 + b_1_0·b_1_1 + b_1_0²
3. b_1_1·b_1_3² + b_1_1²·b_1_3 + b_1_0·b_1_1·b_1_3 + b_1_0·b_1_1² + b_1_0³
4. b_1_0³·b_1_3² + b_1_0³·b_1_1·b_1_3 + b_1_0³·b_1_1² + b_1_0⁴·b_1_3 + b_1_0⁵
5. b_1_0·b_5_76
6. b_5_76² + b_1_1⁷·b_1_2²·b_1_3 + c_8_194·b_1_2²

About the group

Ring generators

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Data used for Benson′s test

• Benson′s completion test succeeded in degree 10.
• The completion test was perfect: It applied in the last degree in which a generator or relation was found.
• The following is a filter regular homogeneous system of parameters:
  1. c_2_13, a Duflot regular element of degree 2
  2. c_8_194, a Duflot regular element of degree 8
  3. b_1_3·b_1_4 + b_1_3² + b_1_2·b_1_4 + b_1_2·b_1_3 + b_1_2² + b_1_1·b_1_2 + b_1_1², an element of degree 2
  4. b_1_2², an element of degree 2
• The Raw Filter Degree Type of that HSOP is [-1, -1, -1, 8, 10].
• The filter degree type of any filter regular HSOP is [-1, -2, -3, -4, -4].

About the group

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Restriction maps

Restriction map to the greatest central el. ab. subgp., which is of rank 2

1. b_1_0 → 0, an element of degree 1
2. b_1_1 → 0, an element of degree 1
3. b_1_2 → 0, an element of degree 1
4. b_1_3 → 0, an element of degree 1
5. b_1_4 → 0, an element of degree 1
6. c_2_13 → c_1_1², an element of degree 2
7. b_5_76 → 0, an element of degree 5
8. c_8_194 → c_1_0⁸, an element of degree 8

Restriction map to a maximal el. ab. subgp. of rank 3

1. b_1_0 → c_1_2, an element of degree 1
2. b_1_1 → c_1_2, an element of degree 1
3. b_1_2 → 0, an element of degree 1
4. b_1_3 → 0, an element of degree 1
5. b_1_4 → 0, an element of degree 1
6. c_2_13 → c_1_1·c_1_2 + c_1_1², an element of degree 2
7. b_5_76 → 0, an element of degree 5
8. c_8_194 → c_1_2⁸ + c_1_0⁴·c_1_2⁴ + c_1_0⁸, an element of degree 8

Restriction map to a maximal el. ab. subgp. of rank 3

1. b_1_0 → c_1_2, an element of degree 1
2. b_1_1 → c_1_2, an element of degree 1
3. b_1_2 → 0, an element of degree 1
4. b_1_3 → 0, an element of degree 1
5. b_1_4 → c_1_2, an element of degree 1
6. c_2_13 → c_1_1·c_1_2 + c_1_1², an element of degree 2
7. b_5_76 → 0, an element of degree 5
8. c_8_194 → c_1_2⁸ + c_1_0⁴·c_1_2⁴ + c_1_0⁸, an element of degree 8

Restriction map to a maximal el. ab. subgp. of rank 4

1. b_1_0 → 0, an element of degree 1
2. b_1_1 → c_1_2, an element of degree 1
3. b_1_2 → c_1_3, an element of degree 1
4. b_1_3 → 0, an element of degree 1
5. b_1_4 → 0, an element of degree 1
6. c_2_13 → c_1_1·c_1_3 + c_1_1², an element of degree 2
7. b_5_76 → c_1_0²·c_1_2²·c_1_3 + c_1_0⁴·c_1_3, an element of degree 5
8. c_8_194 → c_1_0⁴·c_1_2⁴ + c_1_0⁸, an element of degree 8

Restriction map to a maximal el. ab. subgp. of rank 4

1. b_1_0 → 0, an element of degree 1
2. b_1_1 → 0, an element of degree 1
3. b_1_2 → c_1_2, an element of degree 1
4. b_1_3 → c_1_3, an element of degree 1
5. b_1_4 → 0, an element of degree 1
6. c_2_13 → c_1_1·c_1_2 + c_1_1², an element of degree 2
7. b_5_76 → c_1_0²·c_1_2·c_1_3² + c_1_0⁴·c_1_2, an element of degree 5
8. c_8_194 → c_1_0⁴·c_1_3⁴ + c_1_0⁸, an element of degree 8

Restriction map to a maximal el. ab. subgp. of rank 4

1. b_1_0 → 0, an element of degree 1
2. b_1_1 → c_1_3, an element of degree 1
3. b_1_2 → c_1_2, an element of degree 1
4. b_1_3 → c_1_3, an element of degree 1
5. b_1_4 → c_1_3, an element of degree 1
6. c_2_13 → c_1_1·c_1_2 + c_1_1², an element of degree 2
7. b_5_76 → c_1_0²·c_1_2·c_1_3² + c_1_0⁴·c_1_2, an element of degree 5
8. c_8_194 → c_1_3⁸ + c_1_0⁴·c_1_3⁴ + c_1_0⁸, an element of degree 8

About the group

Ring generators

Ring relations

Completion information

Restriction maps

Back to groups of order 128