Simon King
David J. Green
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Cohomology of group number 2189 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 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
( − 1) · (t3 − t2 − t − 1) |
| (t − 1)4 · (t2 + 1)2 |
- The a-invariants are -∞,-∞,-∞,-4,-4. 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_0, a nilpotent element of degree 1
- a_1_1, a nilpotent element of degree 1
- a_1_2, a nilpotent element of degree 1
- b_1_3, an element of degree 1
- c_1_4, a Duflot regular element of degree 1
- b_4_31, an element of degree 4
- c_4_32, a Duflot regular element of degree 4
- c_4_33, a Duflot regular element of degree 4
Ring relations
There are 6 minimal relations of maximal degree 8:
- a_1_22 + a_1_0·a_1_2 + a_1_02
- a_1_0·b_1_3 + a_1_1·a_1_2 + a_1_12 + a_1_0·a_1_1
- a_1_03
- a_1_1·a_1_2·b_1_3 + a_1_12·b_1_3 + a_1_13 + a_1_0·a_1_12 + a_1_02·a_1_1
- b_4_31·a_1_0
- b_4_312 + c_4_32·b_1_34
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_1_4, a Duflot regular element of degree 1
- c_4_32, a Duflot regular element of degree 4
- c_4_33, a Duflot regular element of degree 4
- b_1_32, an element of degree 2
- The Raw Filter Degree Type of that HSOP is [-1, -1, -1, 5, 7].
- 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_1 → 0, an element of degree 1
- a_1_2 → 0, an element of degree 1
- b_1_3 → 0, an element of degree 1
- c_1_4 → c_1_0, an element of degree 1
- b_4_31 → 0, an element of degree 4
- c_4_32 → c_1_24, an element of degree 4
- c_4_33 → 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
- a_1_1 → 0, an element of degree 1
- a_1_2 → 0, an element of degree 1
- b_1_3 → c_1_3, an element of degree 1
- c_1_4 → c_1_0, an element of degree 1
- b_4_31 → c_1_22·c_1_32, an element of degree 4
- c_4_32 → c_1_24, an element of degree 4
- c_4_33 → c_1_22·c_1_32 + c_1_12·c_1_32 + c_1_14, an element of degree 4
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