Simon King
David J. Green
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Singular
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Cohomology of group number 685 of order 128
General information on the group
- The group has 3 minimal generators and exponent 8.
- It is non-abelian.
- It has p-Rank 3.
- Its center has rank 1.
- 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 1.
- The depth coincides with the Duflot bound.
- The Poincaré series is
t6 − t5 − t4 + t3 − 1 |
| (t − 1)3 · (t2 + 1) · (t4 + 1) |
- The a-invariants are -∞,-5,-3,-3. They were obtained using the filter regular HSOP of the Benson test.
Ring generators
The cohomology ring has 11 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_2_3, an element of degree 2
- b_2_4, an element of degree 2
- a_4_3, a nilpotent element of degree 4
- b_5_7, an element of degree 5
- b_5_8, an element of degree 5
- b_5_9, an element of degree 5
- b_8_16, an element of degree 8
- c_8_17, a Duflot regular element of degree 8
Ring relations
There are 30 minimal relations of maximal degree 16:
- a_1_12 + a_1_02
- a_1_0·a_1_1
- a_1_22 + a_1_0·a_1_2
- b_2_4·a_1_0 + b_2_3·a_1_1 + a_1_02·a_1_2
- b_2_3·b_2_4·a_1_1 + b_2_32·a_1_1
- a_4_3·a_1_1
- a_4_3·a_1_0
- a_1_1·b_5_7
- a_1_1·b_5_8 + a_1_0·b_5_7 + b_2_3·a_4_3
- a_1_0·b_5_8 + b_2_3·a_4_3 + b_2_32·a_1_1·a_1_2 + b_2_32·a_1_0·a_1_2
- a_1_1·b_5_9 + b_2_4·a_4_3
- a_1_0·b_5_9 + b_2_3·a_4_3
- b_2_4·b_5_7 + b_2_3·b_5_9 + b_2_3·b_5_8 + b_2_32·b_2_4·a_1_2 + b_2_33·a_1_2
+ b_2_33·a_1_0 + a_1_0·a_1_2·b_5_7
- a_4_32
- a_4_3·b_5_7 + b_2_34·a_1_1 + b_2_34·a_1_0
- a_4_3·b_5_8 + b_2_34·a_1_0 + b_2_3·b_2_4·a_4_3·a_1_2 + b_2_32·a_4_3·a_1_2
- a_4_3·b_5_9 + b_2_34·a_1_0
- b_8_16·a_1_1 + b_2_44·a_1_1 + b_2_34·a_1_1 + b_2_42·a_4_3·a_1_2
- b_8_16·a_1_0 + b_2_34·a_1_1 + b_2_34·a_1_0 + b_2_32·a_4_3·a_1_2
- b_5_82 + b_5_72 + b_2_32·b_2_43 + b_2_34·a_1_1·a_1_2 + b_2_34·a_1_0·a_1_2
- b_5_92 + b_2_3·b_2_44 + b_2_32·b_2_43 + b_2_35 + b_2_43·a_4_3 + b_2_33·a_4_3
- b_5_7·b_5_9 + b_5_7·b_5_8 + b_2_32·b_2_43 + b_2_34·b_2_4 + b_2_32·a_1_2·b_5_9
+ b_2_32·a_1_2·b_5_8 + b_2_32·a_1_2·b_5_7 + b_2_32·b_2_4·a_4_3 + b_2_33·a_4_3 + b_2_34·a_1_0·a_1_2
- b_5_72 + b_2_33·b_2_42 + b_2_35 + b_2_32·b_2_4·a_4_3 + b_2_33·a_4_3
+ c_8_17·a_1_02
- b_5_7·b_5_8 + b_2_3·b_8_16 + b_2_3·b_2_44 + b_2_33·b_2_42 + b_2_3·b_2_4·a_1_2·b_5_9
+ b_2_3·b_2_4·a_1_2·b_5_8 + b_2_32·a_1_2·b_5_8 + b_2_32·a_1_2·b_5_7 + b_2_33·a_4_3
- b_5_8·b_5_9 + b_2_4·b_8_16 + b_2_45 + b_2_33·b_2_42 + b_2_35 + b_2_42·a_1_2·b_5_9
+ b_2_42·a_1_2·b_5_8 + b_2_32·a_1_2·b_5_9 + b_2_34·a_1_0·a_1_2
- a_4_3·b_8_16 + b_2_44·a_4_3 + b_2_34·a_4_3 + b_2_35·a_1_0·a_1_2
- b_8_16·b_5_8 + b_2_44·b_5_8 + b_2_32·b_2_42·b_5_9 + b_2_33·b_2_4·b_5_9
+ b_2_33·b_2_4·b_5_8 + b_2_34·b_5_7 + b_2_42·b_8_16·a_1_2 + b_2_46·a_1_2 + b_2_32·b_8_16·a_1_2 + b_2_35·b_2_4·a_1_2 + b_2_36·a_1_2 + b_2_36·a_1_1 + b_2_33·b_2_4·a_4_3·a_1_2
- b_8_16·b_5_9 + b_2_44·b_5_9 + b_2_3·b_2_43·b_5_8 + b_2_32·b_2_42·b_5_8
+ b_2_33·b_2_4·b_5_9 + b_2_34·b_5_7 + b_2_42·b_8_16·a_1_2 + b_2_46·a_1_2 + b_2_3·b_2_45·a_1_2 + b_2_32·b_2_44·a_1_2 + b_2_34·b_2_42·a_1_2 + b_2_36·a_1_2 + b_2_36·a_1_0 + b_2_44·a_4_3·a_1_2 + b_2_33·b_2_4·a_4_3·a_1_2
- b_8_16·b_5_7 + b_2_3·b_2_43·b_5_9 + b_2_3·b_2_43·b_5_8 + b_2_32·b_2_42·b_5_8
+ b_2_33·b_2_4·b_5_9 + b_2_33·b_2_4·b_5_8 + b_2_34·b_5_8 + b_2_32·b_8_16·a_1_2 + b_2_32·b_2_44·a_1_2 + b_2_33·b_2_43·a_1_2 + b_2_35·b_2_4·a_1_2 + b_2_36·a_1_2 + b_2_33·b_2_4·a_4_3·a_1_2 + b_2_34·a_4_3·a_1_2
- b_8_162 + b_2_48 + b_2_33·b_2_45 + b_2_35·b_2_43 + b_2_38
+ b_2_37·a_1_0·a_1_2
Data used for Benson′s test
- Benson′s completion test succeeded in degree 16.
- 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_8_17, a Duflot regular element of degree 8
- b_2_42 + b_2_3·b_2_4 + b_2_32, an element of degree 4
- b_2_4, an element of degree 2
- The Raw Filter Degree Type of that HSOP is [-1, 3, 9, 11].
- 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 1
- 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_2_3 → 0, an element of degree 2
- b_2_4 → 0, an element of degree 2
- a_4_3 → 0, an element of degree 4
- b_5_7 → 0, an element of degree 5
- b_5_8 → 0, an element of degree 5
- b_5_9 → 0, an element of degree 5
- b_8_16 → 0, an element of degree 8
- c_8_17 → c_1_08, 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_2_3 → c_1_22 + c_1_12, an element of degree 2
- b_2_4 → c_1_22, an element of degree 2
- a_4_3 → 0, an element of degree 4
- b_5_7 → c_1_12·c_1_23 + c_1_13·c_1_22 + c_1_14·c_1_2 + c_1_15, an element of degree 5
- b_5_8 → c_1_25 + c_1_13·c_1_22 + c_1_14·c_1_2 + c_1_15, an element of degree 5
- b_5_9 → c_1_25 + c_1_12·c_1_23 + c_1_14·c_1_2 + c_1_15, an element of degree 5
- b_8_16 → c_1_12·c_1_26 + c_1_13·c_1_25 + c_1_14·c_1_24 + c_1_15·c_1_23 + c_1_18, an element of degree 8
- c_8_17 → c_1_13·c_1_25 + c_1_15·c_1_23 + c_1_02·c_1_12·c_1_24
+ c_1_02·c_1_14·c_1_22 + c_1_04·c_1_24 + c_1_04·c_1_12·c_1_22 + c_1_04·c_1_14 + c_1_08, an element of degree 8
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