Simon King
David J. Green
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Cohomology of group number 2168 of order 128
General information on the group
- The group has 5 minimal generators and exponent 4.
- It is non-abelian.
- It has p-Rank 5.
- Its center has rank 4.
- It has 2 conjugacy classes of maximal elementary abelian subgroups, which are all of rank 5.
Structure of the cohomology ring
General information
- The cohomology ring is of dimension 5 and depth 4.
- The depth coincides with the Duflot bound.
- The Poincaré series is
- The a-invariants are -∞,-∞,-∞,-∞,-5,-5. They were obtained using the filter regular HSOP of the Benson test.
Ring generators
The cohomology ring has 8 minimal generators of maximal degree 4:
- a_1_1, a nilpotent element of degree 1
- b_1_0, an element of degree 1
- b_1_2, an element of degree 1
- c_1_3, a Duflot regular element of degree 1
- c_1_4, a Duflot regular element of degree 1
- c_2_13, a Duflot regular element of degree 2
- b_3_29, an element of degree 3
- c_4_55, a Duflot regular element of degree 4
Ring relations
There are 5 minimal relations of maximal degree 6:
- a_1_1·b_1_0 + a_1_12
- b_1_22 + b_1_0·b_1_2 + a_1_12
- a_1_13
- a_1_1·b_3_29 + c_2_13·a_1_12
- b_3_292 + b_1_02·b_1_2·b_3_29 + b_1_05·b_1_2 + c_4_55·b_1_02
+ c_2_13·b_1_03·b_1_2 + c_2_13·b_1_04 + c_4_55·a_1_12 + c_2_132·b_1_02
Data used for Benson′s test
- Benson′s completion test succeeded in degree 7.
- However, the last relation was already found in degree 6 and the last generator in degree 4.
- The following is a filter regular homogeneous system of parameters:
- c_1_3, a Duflot regular element of degree 1
- c_1_4, a Duflot regular element of degree 1
- c_2_13, a Duflot regular element of degree 2
- c_4_55, a Duflot regular element of degree 4
- b_1_02, an element of degree 2
- The Raw Filter Degree Type of that HSOP is [-1, -1, -1, -1, 3, 5].
- The filter degree type of any filter regular HSOP is [-1, -2, -3, -4, -5, -5].
Restriction maps
Restriction map to the greatest central el. ab. subgp., which is of rank 4
- a_1_1 → 0, an element of degree 1
- b_1_0 → 0, an element of degree 1
- b_1_2 → 0, an element of degree 1
- c_1_3 → c_1_0, an element of degree 1
- c_1_4 → c_1_1, an element of degree 1
- c_2_13 → c_1_32 + c_1_22, an element of degree 2
- b_3_29 → 0, an element of degree 3
- c_4_55 → c_1_24, an element of degree 4
Restriction map to a maximal el. ab. subgp. of rank 5
- a_1_1 → 0, an element of degree 1
- b_1_0 → c_1_4, an element of degree 1
- b_1_2 → 0, an element of degree 1
- c_1_3 → c_1_0, an element of degree 1
- c_1_4 → c_1_1, an element of degree 1
- c_2_13 → c_1_3·c_1_4 + c_1_32 + c_1_2·c_1_4 + c_1_22, an element of degree 2
- b_3_29 → c_1_3·c_1_42 + c_1_32·c_1_4, an element of degree 3
- c_4_55 → c_1_3·c_1_43 + c_1_32·c_1_42 + c_1_2·c_1_43 + c_1_24, an element of degree 4
Restriction map to a maximal el. ab. subgp. of rank 5
- a_1_1 → 0, an element of degree 1
- b_1_0 → c_1_4, an element of degree 1
- b_1_2 → c_1_4, an element of degree 1
- c_1_3 → c_1_0, an element of degree 1
- c_1_4 → c_1_1, an element of degree 1
- c_2_13 → c_1_3·c_1_4 + c_1_32 + c_1_2·c_1_4 + c_1_22, an element of degree 2
- b_3_29 → c_1_43 + c_1_3·c_1_42 + c_1_32·c_1_4, an element of degree 3
- c_4_55 → c_1_44 + c_1_3·c_1_43 + c_1_32·c_1_42 + c_1_22·c_1_42 + c_1_24, an element of degree 4
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