David J. Green

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Cohomology of group number 1627 of order 128

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General information on the group

• The group has 4 minimal generators and exponent 8.
• It is non-abelian.
• It has p-Rank 4.
• Its center has rank 3.
• It has 2 conjugacy classes of maximal elementary abelian subgroups, which are all of rank 4.

Structure of the cohomology ring

General information

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

  1

  (t  −  1)4

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

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Ring generators

The cohomology ring has 8 minimal generators of maximal degree 4:

1. a_1_0, a nilpotent element of degree 1
2. b_1_1, an element of degree 1
3. b_1_2, an element of degree 1
4. c_1_3, a Duflot regular element of degree 1
5. b_2_8, an element of degree 2
6. c_2_9, a Duflot regular element of degree 2
7. a_3_8, a nilpotent element of degree 3
8. c_4_34, a Duflot regular element of degree 4

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Ring relations

There are 9 minimal relations of maximal degree 6:

1. a_1_0²
2. a_1_0·b_1_1
3. b_1_1·b_1_2²
4. b_2_8·a_1_0
5. b_2_8² + c_2_9·b_1_1²
6. b_2_8·b_1_2² + a_1_0·b_1_2³ + a_1_0·a_3_8
7. b_1_1·a_3_8
8. b_2_8·a_3_8 + a_1_0·b_1_2·a_3_8
9. a_3_8² + a_1_0·b_1_2²·a_3_8

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Data used for Benson′s test

• Benson′s completion test succeeded in degree 6.
• 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_1_3, a Duflot regular element of degree 1
  2. c_2_9, a Duflot regular element of degree 2
  3. c_4_34, a Duflot regular element of degree 4
  4. b_1_2² + b_1_1², an element of degree 2
• The Raw Filter Degree Type of that HSOP is [-1, -1, -1, -1, 5].
• The filter degree type of any filter regular HSOP is [-1, -2, -3, -4, -4].

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Restriction maps

Restriction map to the greatest central el. ab. subgp., which is of rank 3

1. a_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. c_1_3 → c_1_0, an element of degree 1
5. b_2_8 → 0, an element of degree 2
6. c_2_9 → c_1_1², an element of degree 2
7. a_3_8 → 0, an element of degree 3
8. c_4_34 → c_1_2⁴, an element of degree 4

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

1. a_1_0 → 0, an element of degree 1
2. b_1_1 → c_1_3, an element of degree 1
3. b_1_2 → 0, an element of degree 1
4. c_1_3 → c_1_0, an element of degree 1
5. b_2_8 → c_1_1·c_1_3, an element of degree 2
6. c_2_9 → c_1_1², an element of degree 2
7. a_3_8 → 0, an element of degree 3
8. c_4_34 → c_1_2²·c_1_3² + c_1_2⁴, an element of degree 4

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

1. a_1_0 → 0, an element of degree 1
2. b_1_1 → 0, an element of degree 1
3. b_1_2 → c_1_3, an element of degree 1
4. c_1_3 → c_1_0, an element of degree 1
5. b_2_8 → 0, an element of degree 2
6. c_2_9 → c_1_1², an element of degree 2
7. a_3_8 → 0, an element of degree 3
8. c_4_34 → c_1_2²·c_1_3² + c_1_2⁴, an element of degree 4

About the group

Ring generators

Ring relations

Completion information

Restriction maps

Back to groups of order 128