Cohomology of group number 887 of order 128

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General information on the group

  • The group has 3 minimal generators and exponent 16.
  • 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.

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Ring generators

The cohomology ring has 10 minimal generators of maximal degree 8:

  1. a_1_0, a nilpotent element of degree 1
  2. a_1_1, a nilpotent element of degree 1
  3. b_1_2, an element of degree 1
  4. b_2_4, an element of degree 2
  5. a_4_4, a nilpotent element of degree 4
  6. a_5_8, a nilpotent element of degree 5
  7. a_5_7, a nilpotent element of degree 5
  8. b_5_9, an element of degree 5
  9. a_8_13, a nilpotent element of degree 8
  10. c_8_17, a Duflot regular element of degree 8

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Ring relations

There are 29 minimal relations of maximal degree 16:

  1. a_1_02
  2. a_1_12 + a_1_0·a_1_1
  3. a_1_0·b_1_22 + b_2_4·a_1_1
  4. b_2_4·a_1_1·b_1_22 + b_2_42·a_1_1
  5. a_4_4·a_1_1
  6. a_4_4·a_1_0
  7. a_1_1·a_5_8 + a_1_0·a_5_8
  8. a_1_1·a_5_7
  9. b_2_4·a_4_4 + a_1_1·a_5_8 + a_1_0·a_5_7
  10. a_1_1·b_5_9 + a_4_4·b_1_22 + a_1_1·a_5_8
  11. a_1_0·b_5_9 + b_2_4·a_4_4 + a_1_1·a_5_8
  12. b_1_22·a_5_7 + b_1_22·a_5_8 + b_2_4·a_5_8
  13. a_4_42
  14. a_4_4·a_5_8
  15. a_4_4·a_5_7
  16. a_4_4·b_5_9
  17. a_8_13·a_1_1
  18. a_8_13·a_1_0
  19. a_5_8·a_5_7
  20. a_5_72 + a_5_82 + b_2_42·a_1_0·a_5_7 + b_2_42·a_1_0·a_5_8
  21. b_5_92 + b_2_4·b_1_28 + b_2_43·b_1_24 + a_5_72
  22. a_5_82 + b_2_42·a_1_0·a_5_8 + c_8_17·a_1_0·a_1_1
  23. a_5_8·b_5_9 + a_8_13·b_1_22 + a_5_82
  24. a_5_7·b_5_9 + a_5_8·b_5_9 + b_2_4·a_8_13 + a_5_72 + b_2_42·a_1_0·a_5_8
  25. a_4_4·a_8_13
  26. a_8_13·a_5_7
  27. a_8_13·a_5_8
  28. a_8_13·b_5_9 + b_2_4·b_1_26·a_5_8 + b_2_43·b_1_22·a_5_8
  29. a_8_132

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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:
    1. c_8_17, a Duflot regular element of degree 8
    2. b_1_24 + b_2_4·b_1_22 + b_2_42, an element of degree 4
    3. b_1_22, 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].

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Restriction maps

Restriction map to the greatest central el. ab. subgp., which is of rank 1

  1. a_1_0 → 0, an element of degree 1
  2. a_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. a_4_4 → 0, an element of degree 4
  6. a_5_8 → 0, an element of degree 5
  7. a_5_7 → 0, an element of degree 5
  8. b_5_9 → 0, an element of degree 5
  9. a_8_13 → 0, an element of degree 8
  10. c_8_17 → c_1_08, an element of degree 8

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

  1. a_1_0 → 0, an element of degree 1
  2. a_1_1 → 0, an element of degree 1
  3. b_1_2 → c_1_2, an element of degree 1
  4. b_2_4 → c_1_12, an element of degree 2
  5. a_4_4 → 0, an element of degree 4
  6. a_5_8 → 0, an element of degree 5
  7. a_5_7 → 0, an element of degree 5
  8. b_5_9 → c_1_1·c_1_24 + c_1_13·c_1_22, an element of degree 5
  9. a_8_13 → 0, an element of degree 8
  10. c_8_17 → 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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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