Cohomology of group number 27 of order 32

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General information on the group

  • The group has 3 minimal generators and exponent 4.
  • It is non-abelian.
  • It has p-Rank 4.
  • Its center has rank 2.
  • It has 2 conjugacy classes of maximal elementary abelian subgroups, which are of rank 3 and 4, respectively.

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
    1
    (t  +  1) · (t  −  1)4
  • 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 6 minimal generators of maximal degree 2:

  1. b_1_0, an element of degree 1
  2. b_1_1, an element of degree 1
  3. b_1_2, an element of degree 1
  4. b_2_4, an element of degree 2
  5. c_2_5, a Duflot regular element of degree 2
  6. c_2_6, a Duflot regular element of degree 2

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Ring relations

There are 4 minimal relations of maximal degree 4:

  1. b_1_0·b_1_1
  2. b_1_0·b_1_2
  3. b_2_4·b_1_0
  4. b_2_4·b_1_1·b_1_2 + b_2_42 + c_2_6·b_1_12 + c_2_5·b_1_22

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Data used for Benson′s test

  • Benson′s completion test succeeded in degree 4.
  • 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:
    1. c_2_5, a Duflot regular element of degree 2
    2. c_2_6, a Duflot regular element of degree 2
    3. b_1_22 + b_1_1·b_1_2 + b_1_12 + b_1_02, an element of degree 2
    4. b_1_2, an element of degree 1
  • The Raw Filter Degree Type of that HSOP is [-1, -1, -1, 2, 3].
  • 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 2

  1. b_1_0 → 0, an element of degree 1
  2. b_1_1 → 0, an element of degree 1
  3. b_1_2 → 0, an element of degree 1
  4. b_2_4 → 0, an element of degree 2
  5. c_2_5 → c_1_02, an element of degree 2
  6. c_2_6 → c_1_12, an element of degree 2

Restriction map to a maximal el. ab. subgp. of rank 3

  1. b_1_0 → c_1_2, an element of degree 1
  2. b_1_1 → 0, an element of degree 1
  3. b_1_2 → 0, an element of degree 1
  4. b_2_4 → 0, an element of degree 2
  5. c_2_5 → c_1_0·c_1_2 + c_1_02, an element of degree 2
  6. c_2_6 → c_1_1·c_1_2 + c_1_12, an element of degree 2

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

  1. b_1_0 → 0, an element of degree 1
  2. b_1_1 → c_1_2, an element of degree 1
  3. b_1_2 → c_1_3, an element of degree 1
  4. b_2_4 → c_1_1·c_1_2 + c_1_0·c_1_3, an element of degree 2
  5. c_2_5 → c_1_0·c_1_2 + c_1_02, an element of degree 2
  6. c_2_6 → c_1_1·c_1_3 + c_1_12, an element of degree 2

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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