Simon King
David J. Green
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Cohomology of group number 2312 of order 128
General information on the group
- The group has 5 minimal generators and exponent 8.
- It is non-abelian.
- It has p-Rank 4.
- Its center has rank 2.
- It has 3 conjugacy classes of maximal elementary abelian subgroups, which are all of rank 4.
Structure of the cohomology ring
General information
- The cohomology ring is of dimension 4 and depth 3.
- The depth exceeds the Duflot bound, which is 2.
- The Poincaré series is
t6 + t5 + t2 + t + 1 |
| (t − 1)4 · (t2 + 1) · (t4 + 1) |
- The a-invariants are -∞,-∞,-∞,-6,-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 8:
- b_1_0, an element of degree 1
- b_1_1, an element of degree 1
- b_1_2, an element of degree 1
- b_1_3, an element of degree 1
- c_1_4, a Duflot regular element of degree 1
- b_5_76, an element of degree 5
- b_5_77, an element of degree 5
- c_8_219, a Duflot regular element of degree 8
Ring relations
There are 9 minimal relations of maximal degree 10:
- b_1_0·b_1_1
- b_1_1·b_1_32 + b_1_0·b_1_32 + b_1_0·b_1_22
- b_1_0·b_1_22·b_1_32 + b_1_0·b_1_24
- b_1_1·b_5_76
- b_1_0·b_5_77
- b_1_32·b_5_77 + b_1_32·b_5_76 + b_1_22·b_5_76
- b_5_76·b_5_77 + b_1_24·b_1_36 + b_1_26·b_1_34
- b_5_762 + b_1_24·b_1_36 + b_1_0·b_1_24·b_5_76 + b_1_0·b_1_29 + b_1_04·b_1_26
+ c_8_219·b_1_02
- b_5_772 + b_1_24·b_1_36 + b_1_28·b_1_32 + b_1_1·b_1_24·b_5_77
+ b_1_12·b_1_23·b_5_77 + b_1_14·b_1_2·b_5_77 + c_8_219·b_1_12
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_1_4, a Duflot regular element of degree 1
- c_8_219, a Duflot regular element of degree 8
- b_1_32 + b_1_2·b_1_3 + b_1_22 + b_1_1·b_1_2 + b_1_12 + b_1_0·b_1_2 + b_1_02, an element of degree 2
- b_1_2·b_1_32 + b_1_22·b_1_3 + b_1_1·b_1_22 + b_1_12·b_1_2 + b_1_0·b_1_22
+ b_1_02·b_1_3, an element of degree 3
- The Raw Filter Degree Type of that HSOP is [-1, -1, -1, 5, 10].
- The filter degree type of any filter regular HSOP is [-1, -2, -3, -4, -4].
- We found that there exists some filter regular HSOP formed by the first 2 terms of the above HSOP, together with 2 elements of degree 2.
Restriction maps
Restriction map to the greatest central el. ab. subgp., which is of rank 2
- b_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_1_3 → 0, an element of degree 1
- c_1_4 → c_1_0, an element of degree 1
- b_5_76 → 0, an element of degree 5
- b_5_77 → 0, an element of degree 5
- c_8_219 → c_1_18, an element of degree 8
Restriction map to a maximal el. ab. subgp. of rank 4
- b_1_0 → c_1_2, an element of degree 1
- b_1_1 → 0, an element of degree 1
- b_1_2 → c_1_3, 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_5_76 → c_1_35 + c_1_12·c_1_23 + c_1_14·c_1_2, an element of degree 5
- b_5_77 → 0, an element of degree 5
- c_8_219 → c_1_22·c_1_36 + c_1_12·c_1_22·c_1_34 + c_1_14·c_1_34 + c_1_14·c_1_24
+ c_1_18, an element of degree 8
Restriction map to a maximal el. ab. subgp. of rank 4
- b_1_0 → 0, an element of degree 1
- b_1_1 → c_1_2, an element of degree 1
- b_1_2 → c_1_3, 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_5_76 → 0, an element of degree 5
- b_5_77 → c_1_12·c_1_23 + c_1_14·c_1_2, an element of degree 5
- c_8_219 → c_1_12·c_1_22·c_1_34 + c_1_12·c_1_23·c_1_33 + c_1_12·c_1_25·c_1_3
+ c_1_14·c_1_34 + c_1_14·c_1_2·c_1_33 + c_1_14·c_1_23·c_1_3 + c_1_14·c_1_24 + c_1_18, an element of degree 8
Restriction map to a maximal el. ab. subgp. of rank 4
- b_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_1_3 → c_1_3, an element of degree 1
- c_1_4 → c_1_0, an element of degree 1
- b_5_76 → c_1_22·c_1_33, an element of degree 5
- b_5_77 → c_1_22·c_1_33 + c_1_24·c_1_3, an element of degree 5
- c_8_219 → c_1_38 + c_1_23·c_1_35 + c_1_24·c_1_34 + c_1_27·c_1_3
+ c_1_12·c_1_22·c_1_34 + c_1_12·c_1_24·c_1_32 + c_1_14·c_1_34 + c_1_14·c_1_22·c_1_32 + c_1_14·c_1_24 + c_1_18, an element of degree 8
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