Simon King
David J. Green
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Cohomology of group number 1682 of order 128
General information on the group
- The group has 4 minimal generators and exponent 8.
- It is non-abelian.
- It has p-Rank 3.
- Its center has rank 2.
- It has a unique conjugacy class of maximal elementary abelian subgroups, which is of rank 3.
Structure of the cohomology ring
General information
- The cohomology ring is of dimension 3 and depth 2.
- The depth coincides with the Duflot bound.
- The Poincaré series is
( − 1) · (t2 + t + 1) |
| (t − 1)3 · (t2 + 1) · (t4 + 1) |
- The a-invariants are -∞,-∞,-3,-3. They were obtained using the filter regular HSOP of the Benson test.
Ring generators
The cohomology ring has 7 minimal generators of maximal degree 8:
- 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_2_8, a Duflot regular element of degree 2
- b_5_26, an element of degree 5
- c_8_45, a Duflot regular element of degree 8
Ring relations
There are 6 minimal relations of maximal degree 10:
- a_1_0·a_1_1
- a_1_22 + a_1_02
- a_1_2·b_1_32 + a_1_0·b_1_32 + a_1_1·a_1_2·b_1_3 + a_1_0·a_1_2·b_1_3 + a_1_02·b_1_3
+ a_1_13 + a_1_03
- a_1_13·b_1_32 + a_1_03·b_1_32 + a_1_14·b_1_3 + a_1_04·b_1_3 + a_1_15 + a_1_05
- a_1_2·b_5_26 + a_1_0·b_5_26 + a_1_06 + c_2_8·a_1_12·a_1_2·b_1_3
+ c_2_8·a_1_02·a_1_2·b_1_3 + c_2_8·a_1_03·b_1_3 + c_2_8·a_1_14
- b_5_262 + c_2_8·b_1_38 + c_2_82·a_1_12·b_1_34 + c_2_82·a_1_05·b_1_3
+ c_2_82·a_1_06
Data used for Benson′s test
- Benson′s completion test succeeded in degree 10.
- 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_8, a Duflot regular element of degree 2
- c_8_45, a Duflot regular element of degree 8
- b_1_32, an element of degree 2
- The Raw Filter Degree Type of that HSOP is [-1, -1, 7, 9].
- The filter degree type of any filter regular HSOP is [-1, -2, -3, -3].
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
- 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_2_8 → c_1_02, an element of degree 2
- b_5_26 → 0, an element of degree 5
- c_8_45 → c_1_18, an element of degree 8
Restriction map to a maximal el. ab. subgp. 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 → c_1_2, an element of degree 1
- c_2_8 → c_1_02, an element of degree 2
- b_5_26 → c_1_0·c_1_24, an element of degree 5
- c_8_45 → c_1_14·c_1_24 + c_1_18 + c_1_0·c_1_27 + c_1_02·c_1_26 + c_1_04·c_1_24
+ c_1_06·c_1_22, an element of degree 8
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