Cohomology of group number 756 of order 128

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

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Ring generators

The cohomology ring has 12 minimal generators of maximal degree 4:

  1. a_1_0, a nilpotent element of degree 1
  2. a_1_1, a nilpotent element of degree 1
  3. a_1_2, a nilpotent element of degree 1
  4. a_2_3, a nilpotent element of degree 2
  5. a_2_4, a nilpotent element of degree 2
  6. c_2_5, a Duflot regular element of degree 2
  7. a_3_7, a nilpotent element of degree 3
  8. a_3_8, a nilpotent element of degree 3
  9. a_3_9, a nilpotent element of degree 3
  10. a_4_11, a nilpotent element of degree 4
  11. c_4_13, a Duflot regular element of degree 4
  12. c_4_14, a Duflot regular element of degree 4

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Ring relations

There are 36 minimal relations of maximal degree 8:

  1. a_1_12 + a_1_0·a_1_1 + a_1_02
  2. a_1_1·a_1_2
  3. a_1_0·a_1_2
  4. a_1_03
  5. a_1_23
  6. a_2_3·a_1_2
  7. a_2_4·a_1_1 + a_2_3·a_1_0
  8. a_2_4·a_1_0 + a_2_3·a_1_1 + a_2_3·a_1_0
  9. a_2_32 + a_2_3·a_1_0·a_1_1 + c_2_5·a_1_02
  10. a_2_3·a_2_4 + a_2_3·a_1_02 + c_2_5·a_1_0·a_1_1 + c_2_5·a_1_02
  11. a_1_1·a_3_7 + a_2_3·a_1_02
  12. a_1_0·a_3_7
  13. a_1_2·a_3_7 + a_2_42 + a_2_3·a_1_0·a_1_1 + a_2_3·a_1_02 + c_2_5·a_1_0·a_1_1
  14. a_1_2·a_3_8
  15. a_1_1·a_3_9 + a_1_1·a_3_8 + a_1_0·a_3_8 + a_2_4·a_1_22
  16. a_1_1·a_3_8 + a_1_0·a_3_9
  17. a_1_2·a_3_9
  18. a_2_3·a_3_7
  19. a_1_02·a_3_8 + a_2_42·a_1_2
  20. a_2_4·a_3_8 + a_2_3·a_3_9 + a_2_3·a_3_8
  21. a_2_4·a_3_9 + a_2_3·a_3_8
  22. a_4_11·a_1_1 + a_2_4·a_3_8 + a_2_3·a_3_8 + a_1_02·a_3_9 + a_2_42·a_1_2
       + a_2_3·c_2_5·a_1_1
  23. a_4_11·a_1_0 + a_2_3·a_3_8 + a_1_02·a_3_9 + a_2_3·c_2_5·a_1_0
  24. a_4_11·a_1_2
  25. a_3_7·a_3_8
  26. a_3_92 + a_3_8·a_3_9 + a_3_82
  27. a_3_7·a_3_9 + a_2_3·a_1_0·a_3_8
  28. a_3_72 + c_4_13·a_1_22
  29. a_3_92 + a_3_82 + c_4_14·a_1_0·a_1_1
  30. a_3_82 + c_4_14·a_1_02
  31. a_2_3·a_4_11 + c_2_5·a_1_0·a_3_8 + a_2_3·c_2_5·a_1_0·a_1_1 + c_2_52·a_1_02
  32. a_2_4·a_4_11 + c_2_5·a_1_0·a_3_9 + c_2_5·a_1_0·a_3_8 + a_2_3·c_2_5·a_1_02
       + c_2_52·a_1_0·a_1_1 + c_2_52·a_1_02
  33. a_4_11·a_3_9 + a_2_3·c_4_14·a_1_1 + a_2_3·c_2_5·a_3_9 + c_4_14·a_1_02·a_1_1
  34. a_4_11·a_3_8 + a_2_3·a_1_02·a_3_9 + a_2_3·c_4_14·a_1_0 + a_2_3·c_2_5·a_3_8
       + c_4_14·a_1_02·a_1_1
  35. a_4_11·a_3_7 + a_2_3·a_1_02·a_3_9
  36. a_4_112 + a_2_3·c_4_14·a_1_0·a_1_1 + c_2_5·c_4_14·a_1_02
       + a_2_3·c_2_52·a_1_0·a_1_1 + c_2_53·a_1_02

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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_2_5, a Duflot regular element of degree 2
    2. c_4_13, a Duflot regular element of degree 4
    3. c_4_14, a Duflot regular element of degree 4
  • The Raw Filter Degree Type of that HSOP is [-1, -1, -1, 7].
  • 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 3

  1. a_1_0 → 0, an element of degree 1
  2. a_1_1 → 0, an element of degree 1
  3. a_1_2 → 0, an element of degree 1
  4. a_2_3 → 0, an element of degree 2
  5. a_2_4 → 0, an element of degree 2
  6. c_2_5 → c_1_12, an element of degree 2
  7. a_3_7 → 0, an element of degree 3
  8. a_3_8 → 0, an element of degree 3
  9. a_3_9 → 0, an element of degree 3
  10. a_4_11 → 0, an element of degree 4
  11. c_4_13 → c_1_04, an element of degree 4
  12. c_4_14 → c_1_24, an element of degree 4

About the group Ring generators Ring relations Completion information Restriction maps Back to groups of order 128


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