Cohomology of group number 28 of order 243

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General information on the group

  • The group has 2 minimal generators and exponent 9.
  • It is non-abelian.
  • It has p-Rank 2.
  • Its center has rank 1.
  • It has 3 conjugacy classes of maximal elementary abelian subgroups, which are all of rank 2.


Structure of the cohomology ring

General information

  • The cohomology ring is of dimension 2 and depth 2.
  • The depth exceeds the Duflot bound, which is 1.
  • The Poincaré series is
    1

    (t  −  1)2
  • The a-invariants are -∞,-∞,-2. They were obtained using the filter regular HSOP of the Benson test.

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Ring generators

The cohomology ring has 11 minimal generators of maximal degree 6:

  1. a_1_0, a nilpotent element of degree 1
  2. a_1_1, a nilpotent element of degree 1
  3. a_2_1, a nilpotent element of degree 2
  4. b_2_0, an element of degree 2
  5. b_2_2, an element of degree 2
  6. a_3_2, a nilpotent element of degree 3
  7. a_3_3, a nilpotent element of degree 3
  8. b_4_4, an element of degree 4
  9. a_5_5, a nilpotent element of degree 5
  10. b_6_5, an element of degree 6
  11. c_6_6, a Duflot regular element of degree 6

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Ring relations

There are 5 "obvious" relations:
   a_1_02, a_1_12, a_3_22, a_3_32, a_5_52

Apart from that, there are 35 minimal relations of maximal degree 12:

  1. a_1_0·a_1_1
  2. a_2_1·a_1_1
  3. a_2_1·a_1_0
  4. b_2_2·a_1_1 + b_2_0·a_1_1
  5. b_2_2·a_1_0 − b_2_0·a_1_1
  6. a_2_12
  7. a_2_1·b_2_0
  8. b_2_22 + b_2_0·b_2_2
  9. a_2_1·b_2_2
  10. a_1_1·a_3_2
  11. a_1_0·a_3_2
  12. b_2_0·a_3_2
  13. b_2_2·a_3_2
  14. a_2_1·a_3_2
  15. a_2_1·a_3_3
  16. b_4_4·a_1_0 + b_2_02·a_1_1
  17. b_2_0·b_4_4 + b_2_02·b_2_2 + b_2_0·a_1_1·a_3_3 + b_2_0·a_1_0·a_3_3
  18. b_2_2·b_4_4 − b_2_02·b_2_2 − a_3_2·a_3_3
  19. a_2_1·b_4_4 + a_3_2·a_3_3
  20.  − a_3_2·a_3_3 + a_1_1·a_5_5 + b_2_0·a_1_1·a_3_3
  21. a_1_0·a_5_5 + b_2_0·a_1_1·a_3_3 − b_2_0·a_1_0·a_3_3
  22. b_2_0·a_5_5 + b_2_0·b_2_2·a_3_3 − b_2_02·a_3_3
  23. b_2_2·a_5_5 + b_2_0·b_2_2·a_3_3
  24. a_2_1·a_5_5
  25. b_6_5·a_1_1 − b_4_4·a_3_2
  26. b_6_5·a_1_0
  27. a_3_3·a_5_5 + b_4_4·a_1_1·a_3_3 − b_2_02·a_1_1·a_3_3
  28. a_3_2·a_5_5 − b_4_4·a_1_1·a_3_3 + b_2_02·a_1_1·a_3_3
  29. b_2_0·b_6_5 + b_2_02·a_1_1·a_3_3
  30. b_2_2·b_6_5 − b_4_4·a_1_1·a_3_3
  31. a_2_1·b_6_5 + b_4_4·a_1_1·a_3_3 − b_2_02·a_1_1·a_3_3
  32. b_6_5·a_3_3 − b_4_4·a_5_5 + b_4_42·a_1_1 + b_2_02·b_2_2·a_3_3 − b_2_04·a_1_1
  33. b_6_5·a_3_2 − b_4_42·a_1_1 + b_2_04·a_1_1
  34. b_6_5·a_5_5 − b_4_42·a_3_3 − b_4_42·a_3_2 − b_2_03·b_2_2·a_3_3
  35. b_6_52 − b_4_43 − b_2_05·b_2_2 + b_4_42·a_1_1·a_3_3 − b_2_04·a_1_1·a_3_3


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Data used for Benson′s test

  • Benson′s completion test succeeded in degree 12.
  • 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_6_6, a Duflot regular element of degree 6
    2. b_4_4 + b_2_0·b_2_2 + b_2_02, an element of degree 4
  • The Raw Filter Degree Type of that HSOP is [-1, -1, 8].
  • The filter degree type of any filter regular HSOP is [-1, -2, -2].


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Restriction maps

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

  1. a_1_00, an element of degree 1
  2. a_1_10, an element of degree 1
  3. a_2_10, an element of degree 2
  4. b_2_00, an element of degree 2
  5. b_2_20, an element of degree 2
  6. a_3_20, an element of degree 3
  7. a_3_30, an element of degree 3
  8. b_4_40, an element of degree 4
  9. a_5_50, an element of degree 5
  10. b_6_50, an element of degree 6
  11. c_6_6 − c_2_03, an element of degree 6

Restriction map to a maximal el. ab. subgp. of rank 2

  1. a_1_0a_1_1, an element of degree 1
  2. a_1_10, an element of degree 1
  3. a_2_10, an element of degree 2
  4. b_2_0c_2_2, an element of degree 2
  5. b_2_20, an element of degree 2
  6. a_3_20, an element of degree 3
  7. a_3_3 − c_2_2·a_1_0 + c_2_1·a_1_1, an element of degree 3
  8. b_4_4 − c_2_2·a_1_0·a_1_1, an element of degree 4
  9. a_5_5 − c_2_22·a_1_0 + c_2_1·c_2_2·a_1_1, an element of degree 5
  10. b_6_50, an element of degree 6
  11. c_6_6c_2_1·c_2_22 − c_2_13, an element of degree 6

Restriction map to a maximal el. ab. subgp. of rank 2

  1. a_1_00, an element of degree 1
  2. a_1_10, an element of degree 1
  3. a_2_10, an element of degree 2
  4. b_2_00, an element of degree 2
  5. b_2_20, an element of degree 2
  6. a_3_20, an element of degree 3
  7. a_3_30, an element of degree 3
  8. b_4_4c_2_22, an element of degree 4
  9. a_5_50, an element of degree 5
  10. b_6_5 − c_2_23, an element of degree 6
  11. c_6_6c_2_1·c_2_22 − c_2_13, an element of degree 6

Restriction map to a maximal el. ab. subgp. of rank 2

  1. a_1_0 − a_1_1, an element of degree 1
  2. a_1_1a_1_1, an element of degree 1
  3. a_2_10, an element of degree 2
  4. b_2_0 − c_2_2, an element of degree 2
  5. b_2_2c_2_2, an element of degree 2
  6. a_3_20, an element of degree 3
  7. a_3_3c_2_2·a_1_1 − c_2_2·a_1_0 + c_2_1·a_1_1, an element of degree 3
  8. b_4_4c_2_22, an element of degree 4
  9. a_5_5c_2_22·a_1_1 − c_2_22·a_1_0 + c_2_1·c_2_2·a_1_1, an element of degree 5
  10. b_6_5c_2_22·a_1_0·a_1_1, an element of degree 6
  11. c_6_6 − c_2_23 + c_2_1·c_2_22 − c_2_13, an element of degree 6


About the group Ring generators Ring relations Completion information Restriction maps Back to groups of order 243




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