Simon King
David J. Green
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Cohomology of group number 621 of order 128
General information on the group
- The group has 3 minimal generators and exponent 4.
- It is non-abelian.
- It has p-Rank 5.
- Its center has rank 2.
- It has 2 conjugacy classes of maximal elementary abelian subgroups, which are of rank 4 and 5, respectively.
Structure of the cohomology ring
General information
- The cohomology ring is of dimension 5 and depth 3.
- The depth exceeds the Duflot bound, which is 2.
- The Poincaré series is
( − 1) · (t4 − t3 + t2 + 1) |
| (t + 1)2 · (t − 1)5 · (t2 + 1) |
- The a-invariants are -∞,-∞,-∞,-5,-5,-5. They were obtained using the filter regular HSOP of the Benson test.
Ring generators
The cohomology ring has 12 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
- b_2_3, an element of degree 2
- b_2_4, an element of degree 2
- b_2_5, an element of degree 2
- b_2_6, an element of degree 2
- c_2_7, a Duflot regular element of degree 2
- b_3_13, an element of degree 3
- b_3_14, an element of degree 3
- b_4_22, an element of degree 4
- c_4_27, a Duflot regular element of degree 4
Ring relations
There are 25 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
- b_2_3·b_1_2
- b_2_3·a_1_0
- b_2_5·b_1_2 + b_2_4·b_1_2
- b_2_4·b_1_2 + b_2_5·a_1_0
- b_2_4·b_1_2 + b_2_6·a_1_0
- b_1_14 + b_2_32 + c_2_7·b_1_12
- b_1_2·b_3_13
- a_1_0·b_3_13
- b_1_1·b_3_13 + b_2_52 + b_2_4·b_2_6
- a_1_0·b_3_14
- b_1_1·b_3_14 + b_2_52 + b_2_4·b_2_6 + b_2_3·b_2_6 + b_2_3·b_2_5
- b_2_6·b_1_13 + b_2_5·b_1_13 + b_2_3·b_3_14 + b_2_3·b_3_13 + b_2_6·c_2_7·b_1_1
+ b_2_5·c_2_7·b_1_1
- b_4_22·b_1_2 + b_2_4·b_2_5·a_1_0
- b_4_22·a_1_0 + b_2_4·b_2_5·a_1_0
- b_4_22·b_1_1 + b_2_4·b_2_6·b_1_1 + b_2_3·b_3_13
- b_3_142 + b_3_132 + b_2_62·b_1_12 + b_2_52·b_1_12 + b_2_62·c_2_7
+ b_2_52·c_2_7
- b_3_132 + b_2_52·b_2_6 + b_2_53 + b_2_4·b_2_5·b_2_6 + b_2_4·b_2_52
+ c_4_27·b_1_12
- b_2_52·b_1_12 + b_2_4·b_2_6·b_1_12 + b_2_3·b_4_22 + b_2_3·b_2_4·b_2_6
+ b_2_52·c_2_7 + b_2_4·b_2_6·c_2_7
- b_3_13·b_3_14 + b_3_132 + b_2_6·b_4_22 + b_2_5·b_4_22 + b_2_4·b_2_62
+ b_2_4·b_2_5·b_2_6
- b_4_22·b_3_13 + b_2_4·b_2_6·b_3_14 + b_2_4·b_2_5·b_3_14 + b_2_4·b_2_5·b_3_13
+ b_2_3·b_2_6·b_3_13 + b_2_3·b_2_5·b_3_13 + b_2_3·c_4_27·b_1_1
- b_4_22·b_3_14 + b_2_52·b_2_6·b_1_1 + b_2_53·b_1_1 + b_2_4·b_2_6·b_3_13
+ b_2_4·b_2_62·b_1_1 + b_2_4·b_2_5·b_3_14 + b_2_4·b_2_5·b_3_13 + b_2_4·b_2_5·b_2_6·b_1_1 + b_2_3·b_2_6·b_3_13 + b_2_3·b_2_5·b_3_13 + b_2_6·c_2_7·b_3_13 + b_2_5·c_2_7·b_3_13 + b_2_3·c_4_27·b_1_1
- b_4_222 + b_2_4·b_2_62·b_1_12 + b_2_42·b_2_6·b_1_12 + b_2_42·b_2_62
+ b_2_3·b_2_6·b_4_22 + b_2_3·b_2_5·b_4_22 + b_2_3·b_2_4·b_4_22 + b_2_3·b_2_4·b_2_62 + b_2_3·b_2_4·b_2_5·b_2_6 + b_2_3·b_2_42·b_2_6 + b_2_4·b_2_62·c_2_7 + b_2_42·b_2_6·c_2_7 + b_2_32·c_4_27
Data used for Benson′s test
- Benson′s completion test succeeded in degree 13.
- However, the last relation was already found in degree 8 and the last generator in degree 4.
- The following is a filter regular homogeneous system of parameters:
- c_2_7, a Duflot regular element of degree 2
- c_4_27, a Duflot regular element of degree 4
- b_1_24 + b_2_62 + b_2_4·b_2_6 + b_2_42 + b_2_32 + c_2_7·b_1_12, an element of degree 4
- b_2_62·b_1_22 + b_2_62·b_1_12 + b_2_4·b_2_6·b_1_12 + b_2_4·b_2_62
+ b_2_42·b_1_12 + b_2_42·b_2_6, an element of degree 6
- b_1_12, an element of degree 2
- The Raw Filter Degree Type of that HSOP is [-1, -1, -1, 5, 11, 13].
- 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 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
- b_2_3 → 0, an element of degree 2
- b_2_4 → 0, an element of degree 2
- b_2_5 → 0, an element of degree 2
- b_2_6 → 0, an element of degree 2
- c_2_7 → c_1_12, an element of degree 2
- b_3_13 → 0, an element of degree 3
- b_3_14 → 0, an element of degree 3
- b_4_22 → 0, an element of degree 4
- c_4_27 → 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
- b_1_1 → 0, an element of degree 1
- b_1_2 → c_1_2, an element of degree 1
- b_2_3 → 0, an element of degree 2
- b_2_4 → 0, an element of degree 2
- b_2_5 → 0, an element of degree 2
- b_2_6 → c_1_32 + c_1_2·c_1_3, an element of degree 2
- c_2_7 → c_1_12, an element of degree 2
- b_3_13 → 0, an element of degree 3
- b_3_14 → c_1_1·c_1_32 + c_1_1·c_1_2·c_1_3, an element of degree 3
- b_4_22 → 0, an element of degree 4
- c_4_27 → c_1_0·c_1_2·c_1_32 + c_1_0·c_1_22·c_1_3 + c_1_02·c_1_32 + c_1_02·c_1_2·c_1_3
+ c_1_02·c_1_22 + c_1_04, an element of degree 4
Restriction map to a maximal el. ab. subgp. of rank 5
- a_1_0 → 0, an element of degree 1
- b_1_1 → c_1_4, an element of degree 1
- b_1_2 → 0, an element of degree 1
- b_2_3 → c_1_1·c_1_4, an element of degree 2
- b_2_4 → c_1_2·c_1_4 + c_1_22, an element of degree 2
- b_2_5 → c_1_3·c_1_4 + c_1_2·c_1_3 + c_1_0·c_1_4, an element of degree 2
- b_2_6 → c_1_3·c_1_4 + c_1_32, an element of degree 2
- c_2_7 → c_1_42 + c_1_12, an element of degree 2
- b_3_13 → c_1_32·c_1_4 + c_1_2·c_1_3·c_1_4 + c_1_2·c_1_32 + c_1_22·c_1_3 + c_1_02·c_1_4, an element of degree 3
- b_3_14 → c_1_32·c_1_4 + c_1_2·c_1_3·c_1_4 + c_1_2·c_1_32 + c_1_22·c_1_3 + c_1_1·c_1_32
+ c_1_1·c_1_2·c_1_3 + c_1_0·c_1_1·c_1_4 + c_1_02·c_1_4, an element of degree 3
- b_4_22 → c_1_2·c_1_3·c_1_42 + c_1_2·c_1_32·c_1_4 + c_1_22·c_1_3·c_1_4 + c_1_22·c_1_32
+ c_1_1·c_1_32·c_1_4 + c_1_1·c_1_2·c_1_3·c_1_4 + c_1_1·c_1_2·c_1_32 + c_1_1·c_1_22·c_1_3 + c_1_02·c_1_1·c_1_4, an element of degree 4
- c_4_27 → c_1_0·c_1_32·c_1_4 + c_1_0·c_1_2·c_1_3·c_1_4 + c_1_0·c_1_2·c_1_32
+ c_1_0·c_1_22·c_1_3 + c_1_02·c_1_32 + c_1_02·c_1_2·c_1_4 + c_1_02·c_1_2·c_1_3 + c_1_02·c_1_22 + c_1_03·c_1_4 + c_1_04, an element of degree 4
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