Simon King
David J. Green
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Cohomology of group number 555 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 3.
- It has a unique conjugacy class of maximal elementary abelian subgroups, which is of rank 4.
Structure of the cohomology ring
General information
- The cohomology ring is of dimension 4 and depth 3.
- The depth coincides with the Duflot bound.
- 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
- a_1_2, a nilpotent element of degree 1
- b_1_1, an element of degree 1
- a_2_3, a nilpotent element of degree 2
- b_2_4, an element of degree 2
- c_2_5, a Duflot regular element of degree 2
- c_2_6, a Duflot regular element of degree 2
- a_3_4, a nilpotent element of degree 3
- a_3_12, a nilpotent element of degree 3
- a_4_17, a nilpotent element of degree 4
- c_4_20, a Duflot regular element of degree 4
Ring relations
There are 27 minimal relations of maximal degree 8:
- a_1_02
- a_1_0·a_1_2
- a_1_0·b_1_1 + a_1_22
- a_1_22·b_1_1
- a_2_3·a_1_0
- b_2_4·a_1_0 + a_2_3·a_1_2
- b_2_4·a_1_2 + a_2_3·b_1_1
- a_2_32 + c_2_5·a_1_22
- b_2_42 + a_2_3·a_1_2·b_1_1 + c_2_5·b_1_12
- a_2_3·b_2_4 + c_2_5·a_1_2·b_1_1
- a_1_0·a_3_4 + a_2_3·a_1_2·b_1_1
- a_1_2·a_3_4
- a_1_0·a_3_12
- b_1_1·a_3_4 + a_1_2·a_3_12
- a_2_3·a_3_4
- b_2_4·a_3_4 + a_2_3·a_3_12
- a_4_17·b_1_1 + b_2_4·a_3_12 + c_2_5·a_1_2·b_1_12
- a_4_17·a_1_0
- b_2_4·a_3_4 + a_4_17·a_1_2
- a_3_42
- a_3_4·a_3_12
- a_3_122 + a_1_2·b_1_12·a_3_12 + c_4_20·a_1_22
- b_2_4·a_4_17 + c_2_5·b_1_1·a_3_12 + a_2_3·c_2_5·b_1_12
- a_2_3·a_4_17 + c_2_5·a_1_2·a_3_12 + a_2_3·c_2_5·a_1_2·b_1_1
- a_4_17·a_3_4
- a_4_17·a_3_12 + a_2_3·b_1_12·a_3_12 + c_2_5·a_1_2·b_1_1·a_3_12 + a_2_3·c_4_20·a_1_2
- a_4_172 + c_2_5·a_1_2·b_1_12·a_3_12 + c_2_5·c_4_20·a_1_22
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_2_6, a Duflot regular element of degree 2
- c_4_20, a Duflot regular element of degree 4
- b_1_12, an element of degree 2
- The Raw Filter Degree Type of that HSOP is [-1, -1, -1, 4, 6].
- 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 3
- a_1_0 → 0, an element of degree 1
- a_1_2 → 0, an element of degree 1
- b_1_1 → 0, an element of degree 1
- a_2_3 → 0, an element of degree 2
- b_2_4 → 0, an element of degree 2
- c_2_5 → c_1_12, an element of degree 2
- c_2_6 → c_1_22, an element of degree 2
- a_3_4 → 0, an element of degree 3
- a_3_12 → 0, an element of degree 3
- a_4_17 → 0, an element of degree 4
- c_4_20 → c_1_04, 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
- a_1_2 → 0, an element of degree 1
- b_1_1 → c_1_3, an element of degree 1
- a_2_3 → 0, an element of degree 2
- b_2_4 → c_1_1·c_1_3, an element of degree 2
- c_2_5 → c_1_12, an element of degree 2
- c_2_6 → c_1_22, an element of degree 2
- a_3_4 → 0, an element of degree 3
- a_3_12 → 0, an element of degree 3
- a_4_17 → 0, an element of degree 4
- c_4_20 → c_1_02·c_1_32 + c_1_04, an element of degree 4
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