Cohomology of group number 1729 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 5.
  • Its center has rank 3.
  • It has a unique conjugacy class of maximal elementary abelian subgroups, which is of rank 5.

Structure of the cohomology ring

General information

  • The cohomology ring is of dimension 5 and depth 3.
  • The depth coincides with the Duflot bound.
  • The Poincaré series is
    ( − 1) · (t2  −  t  +  1)
    (t  −  1)5 · (t2  +  1)
  • The a-invariants are -∞,-∞,-∞,-5,-5,-5. They were obtained using the filter regular HSOP of the Benson test.

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Ring generators

The cohomology ring has 10 minimal generators of maximal degree 4:

  1. a_1_0, a nilpotent element of degree 1
  2. b_1_1, an element of degree 1
  3. b_1_2, an element of degree 1
  4. c_1_3, a Duflot regular element of degree 1
  5. b_2_8, an element of degree 2
  6. c_2_9, a Duflot regular element of degree 2
  7. b_3_19, an element of degree 3
  8. b_3_20, an element of degree 3
  9. b_4_37, an element of degree 4
  10. c_4_39, a Duflot regular element of degree 4

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Ring relations

There are 18 minimal relations of maximal degree 8:

  1. a_1_0·b_1_1
  2. a_1_0·b_1_2
  3. a_1_03
  4. b_2_8·a_1_0
  5. b_2_8·b_1_1·b_1_2 + b_2_82 + c_2_9·b_1_12
  6. a_1_0·b_3_19
  7. a_1_0·b_3_20
  8. b_1_2·b_3_19 + b_1_1·b_3_20
  9. b_4_37·b_1_2 + b_2_8·b_3_20
  10. b_4_37·a_1_0
  11. b_4_37·b_1_1 + b_2_8·b_3_19
  12. b_3_202 + c_4_39·b_1_22
  13. b_3_19·b_3_20 + c_4_39·b_1_1·b_1_2
  14. b_3_192 + c_4_39·b_1_12
  15. b_2_8·b_1_1·b_3_20 + b_2_8·b_4_37 + c_2_9·b_1_1·b_3_19
  16. b_4_37·b_3_19 + b_2_8·c_4_39·b_1_1
  17. b_4_37·b_3_20 + b_2_8·c_4_39·b_1_2
  18. b_4_372 + b_2_82·c_4_39

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Data used for Benson′s test

  • Benson′s completion test succeeded in degree 8.
  • 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_1_3, a Duflot regular element of degree 1
    2. c_2_9, a Duflot regular element of degree 2
    3. c_4_39, a Duflot regular element of degree 4
    4. b_1_22 + b_1_1·b_1_2 + b_1_12, an element of degree 2
    5. b_1_22, an element of degree 2
  • The Raw Filter Degree Type of that HSOP is [-1, -1, -1, 2, 4, 6].
  • The filter degree type of any filter regular HSOP is [-1, -2, -3, -4, -5, -5].

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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. b_1_1 → 0, an element of degree 1
  3. b_1_2 → 0, an element of degree 1
  4. c_1_3 → c_1_0, an element of degree 1
  5. b_2_8 → 0, an element of degree 2
  6. c_2_9 → c_1_12, an element of degree 2
  7. b_3_19 → 0, an element of degree 3
  8. b_3_20 → 0, an element of degree 3
  9. b_4_37 → 0, an element of degree 4
  10. c_4_39 → c_1_24, an element of degree 4

Restriction map to a maximal el. ab. subgp. of rank 5

  1. a_1_0 → 0, an element of degree 1
  2. b_1_1 → c_1_3, an element of degree 1
  3. b_1_2 → c_1_4, an element of degree 1
  4. c_1_3 → c_1_0, an element of degree 1
  5. b_2_8 → c_1_1·c_1_3, an element of degree 2
  6. c_2_9 → c_1_1·c_1_4 + c_1_12, an element of degree 2
  7. b_3_19 → c_1_2·c_1_32 + c_1_22·c_1_3, an element of degree 3
  8. b_3_20 → c_1_2·c_1_3·c_1_4 + c_1_22·c_1_4, an element of degree 3
  9. b_4_37 → c_1_1·c_1_2·c_1_32 + c_1_1·c_1_22·c_1_3, an element of degree 4
  10. c_4_39 → 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