Cohomology of group number 1651 of order 128

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General information on the group

  • The group has 4 minimal generators and exponent 8.
  • 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) · (t4  −  t3  −  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.

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Ring generators

The cohomology ring has 9 minimal generators of maximal degree 4:

  1. a_1_0, a nilpotent element of degree 1
  2. a_1_2, a nilpotent element of degree 1
  3. b_1_1, an element of degree 1
  4. c_1_3, a Duflot regular element of degree 1
  5. a_3_10, a nilpotent element of degree 3
  6. a_3_11, a nilpotent element of degree 3
  7. b_3_12, an element of degree 3
  8. c_4_19, a Duflot regular element of degree 4
  9. c_4_20, a Duflot regular element of degree 4

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Ring relations

There are 14 minimal relations of maximal degree 6:

  1. a_1_02
  2. a_1_0·b_1_1 + a_1_22
  3. a_1_2·b_1_12
  4. a_1_22·b_1_1
  5. a_1_0·a_3_10
  6. a_1_2·a_3_10 + a_1_0·a_3_11
  7. a_1_0·b_3_12 + a_1_2·a_3_11
  8. b_1_1·a_3_11 + b_1_1·a_3_10 + a_1_2·b_3_12 + a_1_2·a_3_11
  9. a_1_2·b_1_1·b_3_12 + a_1_22·b_3_12
  10. a_3_102
  11. a_3_10·a_3_11 + c_4_19·a_1_0·a_1_2
  12. a_3_112 + c_4_19·a_1_22
  13. a_3_11·b_3_12 + a_3_10·b_3_12 + a_3_112 + c_4_19·a_1_2·b_1_1 + c_4_20·a_1_0·a_1_2
  14. b_3_122 + c_4_19·b_1_12 + c_4_20·a_1_22

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Data used for Benson′s test

  • Benson′s completion test succeeded in degree 8.
  • However, the last relation was already found in degree 6 and the last generator in degree 4.
  • The following is a filter regular homogeneous system of parameters:
    1. c_1_3, a Duflot regular element of degree 1
    2. c_4_19, a Duflot regular element of degree 4
    3. c_4_20, a Duflot regular element of degree 4
    4. b_1_12, 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].

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Restriction maps

Restriction map to the greatest central el. ab. subgp., which is of rank 3

  1. a_1_0 → 0, an element of degree 1
  2. a_1_2 → 0, an element of degree 1
  3. b_1_1 → 0, an element of degree 1
  4. c_1_3 → c_1_0, an element of degree 1
  5. a_3_10 → 0, an element of degree 3
  6. a_3_11 → 0, an element of degree 3
  7. b_3_12 → 0, an element of degree 3
  8. c_4_19 → c_1_14, an element of degree 4
  9. c_4_20 → c_1_24, an element of degree 4

Restriction map to a maximal el. ab. subgp. of rank 4

  1. a_1_0 → 0, an element of degree 1
  2. a_1_2 → 0, an element of degree 1
  3. b_1_1 → c_1_3, an element of degree 1
  4. c_1_3 → c_1_0, an element of degree 1
  5. a_3_10 → 0, an element of degree 3
  6. a_3_11 → 0, an element of degree 3
  7. b_3_12 → c_1_1·c_1_32 + c_1_12·c_1_3, an element of degree 3
  8. c_4_19 → c_1_12·c_1_32 + c_1_14, an element of degree 4
  9. c_4_20 → c_1_22·c_1_32 + c_1_24, an element of degree 4

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Simon A. King David J. Green
Fakultät für Mathematik und Informatik Fakultät für Mathematik und Informatik
Friedrich-Schiller-Universität Jena Friedrich-Schiller-Universität Jena
Ernst-Abbe-Platz 2 Ernst-Abbe-Platz 2
D-07743 Jena D-07743 Jena
Germany Germany
E-mail: simon dot king at uni hyphen jena dot de
Tel: +49 (0)3641 9-46184
Fax: +49 (0)3641 9-46162
Office: Zi. 3524, Ernst-Abbe-Platz 2
E-mail: david dot green at uni hyphen jena dot de
Tel: +49 3641 9-46166
Fax: +49 3641 9-46162
Office: Zi 3512, Ernst-Abbe-Platz 2

Last change: 25.08.2009