Simon King
David J. Green
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Cohomology of group number 628 of order 128
General information on the group
- The group has 3 minimal generators and exponent 8.
- It is non-abelian.
- It has p-Rank 4.
- Its center has rank 2.
- It has 2 conjugacy classes of maximal elementary abelian subgroups, which are of rank 3 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
- The a-invariants are -∞,-∞,-∞,-4,-4. They were obtained using the filter regular HSOP of the Benson test.
Ring generators
The cohomology ring has 11 minimal generators of maximal degree 4:
- a_1_0, a nilpotent element of degree 1
- b_1_1, an element of degree 1
- b_1_2, an element of degree 1
- a_2_3, a nilpotent element of degree 2
- a_2_4, a nilpotent element of degree 2
- b_2_6, an element of degree 2
- c_2_5, a Duflot regular element of degree 2
- a_3_11, a nilpotent element of degree 3
- b_3_12, an element of degree 3
- a_4_17, a nilpotent element of degree 4
- c_4_21, a Duflot regular element of degree 4
Ring relations
There are 27 minimal relations of maximal degree 8:
- a_1_02
- a_1_0·b_1_1
- b_1_1·b_1_2 + a_1_0·b_1_2
- a_2_3·a_1_0
- a_2_3·b_1_2 + a_2_4·a_1_0
- a_2_4·b_1_1 + a_2_3·b_1_2
- b_1_13 + b_2_6·b_1_1 + b_2_6·a_1_0
- a_2_32
- a_2_3·a_2_4
- a_2_42
- a_2_3·b_1_12 + a_2_3·b_2_6 + a_1_0·a_3_11
- b_1_1·a_3_11 + a_2_3·b_1_12 + a_2_3·b_2_6
- b_1_2·a_3_11 + a_1_0·b_3_12 + a_2_4·b_2_6
- b_1_1·b_3_12 + b_1_2·a_3_11 + a_2_4·b_2_6
- a_2_3·a_3_11
- a_2_3·b_3_12 + a_2_4·a_3_11
- a_1_0·b_1_2·b_3_12 + a_4_17·b_1_2 + a_2_4·b_3_12 + a_2_4·b_2_6·b_1_2 + b_2_6·c_2_5·a_1_0
- a_4_17·a_1_0 + a_2_4·a_3_11 + a_2_4·b_2_6·a_1_0
- a_4_17·b_1_1 + a_2_4·a_3_11 + a_2_4·b_2_6·a_1_0
- a_3_112
- b_3_122 + b_2_6·b_1_2·b_3_12 + c_4_21·b_1_22 + b_2_6·c_2_5·b_1_12 + b_2_62·c_2_5
- a_3_11·b_3_12 + b_2_6·a_4_17 + a_2_4·b_2_62 + c_4_21·a_1_0·b_1_2
- a_2_3·a_4_17
- a_2_4·a_1_0·b_3_12 + a_2_4·a_4_17 + c_2_5·a_1_0·a_3_11
- a_4_17·b_3_12 + b_2_6·a_4_17·b_1_2 + a_2_4·b_2_6·b_3_12 + a_2_4·b_2_62·b_1_2
+ c_4_21·a_1_0·b_1_22 + b_2_6·c_2_5·a_3_11 + a_2_4·c_4_21·b_1_2
- a_4_17·a_3_11 + a_2_4·b_2_6·a_3_11 + a_2_4·c_4_21·a_1_0
- a_4_172
Data used for Benson′s test
- Benson′s completion test succeeded in degree 8.
- 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:
- c_2_5, a Duflot regular element of degree 2
- c_4_21, a Duflot regular element of degree 4
- b_1_24 + b_2_6·b_1_22 + b_2_62, an element of degree 4
- b_1_22, an element of degree 2
- The Raw Filter Degree Type of that HSOP is [-1, -1, -1, 6, 8].
- The filter degree type of any filter regular HSOP is [-1, -2, -3, -4, -4].
Restriction maps
Restriction map to the greatest central el. ab. subgp., which is of rank 2
- a_1_0 → 0, an element of degree 1
- b_1_1 → 0, an element of degree 1
- b_1_2 → 0, an element of degree 1
- a_2_3 → 0, an element of degree 2
- a_2_4 → 0, an element of degree 2
- b_2_6 → 0, an element of degree 2
- c_2_5 → c_1_02, an element of degree 2
- a_3_11 → 0, an element of degree 3
- b_3_12 → 0, an element of degree 3
- a_4_17 → 0, an element of degree 4
- c_4_21 → c_1_14, an element of degree 4
Restriction map to a maximal el. ab. subgp. of rank 3
- a_1_0 → 0, an element of degree 1
- b_1_1 → c_1_2, an element of degree 1
- b_1_2 → 0, an element of degree 1
- a_2_3 → 0, an element of degree 2
- a_2_4 → 0, an element of degree 2
- b_2_6 → c_1_22, an element of degree 2
- c_2_5 → c_1_0·c_1_2 + c_1_02, an element of degree 2
- a_3_11 → 0, an element of degree 3
- b_3_12 → 0, an element of degree 3
- a_4_17 → 0, an element of degree 4
- c_4_21 → c_1_12·c_1_22 + c_1_14, an element of degree 4
Restriction map to a maximal el. ab. subgp. of rank 4
- a_1_0 → 0, an element of degree 1
- b_1_1 → 0, an element of degree 1
- b_1_2 → c_1_2, an element of degree 1
- a_2_3 → 0, an element of degree 2
- a_2_4 → 0, an element of degree 2
- b_2_6 → c_1_32, an element of degree 2
- c_2_5 → c_1_0·c_1_2 + c_1_02, an element of degree 2
- a_3_11 → 0, an element of degree 3
- b_3_12 → c_1_12·c_1_2 + c_1_0·c_1_32, an element of degree 3
- a_4_17 → 0, an element of degree 4
- c_4_21 → c_1_12·c_1_32 + c_1_14, an element of degree 4
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