Cohomology of group number 7 of order 81

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General information on the group

  • The group is also known as Syl3(A9), the Sylow 3-subgroup of A_9.
  • The group has 2 minimal generators and exponent 9.
  • It is non-abelian.
  • It has p-Rank 3.
  • Its center has rank 1.
  • It has 2 conjugacy classes of maximal elementary abelian subgroups, which are of rank 2 and 3, respectively.

Structure of the cohomology ring

General information

  • The cohomology ring is of dimension 3 and depth 2.
  • The depth exceeds the Duflot bound, which is 1.
  • The Poincaré series is
     − 1
    (t  −  1)3 · (t2  +  t  +  1)
  • The a-invariants are -∞,-∞,-3,-3. They were obtained using the filter regular HSOP of the Benson test.

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Ring generators

The cohomology ring has 16 minimal generators of maximal degree 7:

  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. a_3_4, a nilpotent element of degree 3
  9. a_4_5, a nilpotent element of degree 4
  10. b_4_6, an element of degree 4
  11. a_5_7, a nilpotent element of degree 5
  12. a_5_8, a nilpotent element of degree 5
  13. a_6_9, a nilpotent element of degree 6
  14. b_6_10, an element of degree 6
  15. c_6_11, a Duflot regular element of degree 6
  16. a_7_14, a nilpotent element of degree 7

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Ring relations

There are 8 "obvious" relations:
   a_1_02, a_1_12, a_3_22, a_3_32, a_3_42, a_5_72, a_5_82, a_7_142

Apart from that, there are 80 minimal relations of maximal degree 13:

  1. a_1_0·a_1_1
  2. a_2_1·a_1_1
  3. a_2_1·a_1_0
  4. b_2_0·a_1_1
  5. b_2_2·a_1_0
  6. a_2_12
  7. a_2_1·b_2_0
  8. b_2_0·b_2_2
  9.  − a_2_1·b_2_2 + a_1_1·a_3_2
  10. a_1_0·a_3_2
  11. a_1_1·a_3_3
  12. a_1_0·a_3_4
  13. b_2_0·a_3_2
  14. a_2_1·a_3_2
  15. a_2_1·a_3_3
  16. b_2_0·a_3_4
  17.  − b_2_2·a_3_3 + a_2_1·a_3_4
  18.  − b_2_2·a_3_3 + a_4_5·a_1_1
  19. a_4_5·a_1_0
  20. b_4_6·a_1_0
  21. a_3_2·a_3_3
  22. a_3_3·a_3_4
  23. b_2_0·a_4_5
  24. a_2_1·a_4_5
  25. b_2_0·b_4_6
  26.  − b_2_2·a_4_5 + a_2_1·b_4_6 + a_3_2·a_3_4
  27.  − b_2_2·a_4_5 + a_3_2·a_3_4 + a_1_1·a_5_7
  28. a_1_0·a_5_7
  29. a_1_0·a_5_8
  30. a_4_5·a_3_3
  31. a_4_5·a_3_2
  32. b_4_6·a_3_3 − a_4_5·a_3_4
  33. b_2_0·a_5_7
  34. a_2_1·a_5_7
  35. b_2_0·a_5_8
  36.  − a_4_5·a_3_4 + a_2_1·a_5_8
  37. a_6_9·a_1_1 − a_4_5·a_3_4
  38. a_6_9·a_1_0
  39. b_6_10·a_1_1 + b_4_6·a_3_2 − b_2_2·a_5_7
  40. b_6_10·a_1_0
  41. a_4_52
  42. a_3_3·a_5_7
  43. a_3_3·a_5_8
  44. a_3_2·a_5_7 − b_4_6·a_1_1·a_3_4 + b_2_2·a_1_1·a_5_8 + b_2_2·a_1_1·a_5_7
  45.  − a_4_5·b_4_6 + a_3_2·a_5_8
  46. b_2_0·a_6_9
  47. b_2_2·a_6_9 + a_3_4·a_5_7 + a_3_2·a_5_7
  48. a_2_1·a_6_9
  49. b_2_0·b_6_10
  50. a_2_1·b_6_10 + a_3_2·a_5_7
  51. a_4_5·b_4_6 + a_3_4·a_5_7 + a_3_2·a_5_7 + a_1_1·a_7_14
  52. a_1_0·a_7_14
  53. a_4_5·a_5_8
  54.  − a_4_5·a_5_7 − a_1_1·a_3_4·a_5_8 + a_1_1·a_3_2·a_5_8
  55. a_6_9·a_3_3
  56. a_6_9·a_3_4 − a_4_5·a_5_7
  57. a_6_9·a_3_2 + a_4_5·a_5_7
  58. b_6_10·a_3_3 − a_4_5·a_5_7
  59. b_6_10·a_3_2 − b_4_62·a_1_1 + b_2_2·b_4_6·a_3_4 − b_2_2·b_4_6·a_3_2 − b_2_22·a_5_8
  60. b_2_0·a_7_14
  61.  − b_6_10·a_3_4 + b_4_6·a_5_7 − b_4_62·a_1_1 + b_2_2·a_7_14 + b_2_2·b_4_6·a_3_4
       − b_2_2·b_4_6·a_3_2 − b_2_22·a_5_8
  62.  − a_4_5·a_5_7 + a_2_1·a_7_14
  63. a_4_5·a_6_9
  64. b_4_6·a_6_9 − a_5_7·a_5_8 − c_6_11·a_1_1·a_3_2
  65. a_4_5·b_6_10 − b_4_6·a_1_1·a_5_8 + b_2_2·a_3_4·a_5_8 − b_2_2·a_3_2·a_5_8
  66. a_3_3·a_7_14
  67.  − a_5_7·a_5_8 + a_3_4·a_7_14 + b_4_6·a_1_1·a_5_8 − b_2_2·a_3_4·a_5_8 + b_2_2·a_3_2·a_5_8
       − c_6_11·a_1_1·a_3_2
  68. a_3_2·a_7_14 − b_4_6·a_1_1·a_5_8 + b_2_2·a_3_4·a_5_8 − b_2_2·a_3_2·a_5_8
  69. a_6_9·a_5_7
  70. a_6_9·a_5_8 − a_2_1·c_6_11·a_3_4
  71. b_6_10·a_5_7 + b_4_62·a_3_4 + b_4_62·a_3_2 − b_2_2·b_4_6·a_5_8 + b_2_2·b_4_6·a_5_7
       + b_2_22·c_6_11·a_1_1
  72. a_4_5·a_7_14
  73.  − b_6_10·a_5_8 + b_4_6·a_7_14 − b_2_2·c_6_11·a_3_2
  74. a_6_92
  75. b_6_102 + b_4_63 + b_2_2·b_4_6·b_6_10 + b_2_23·c_6_11
  76.  − a_6_9·b_6_10 + a_5_7·a_7_14
  77.  − a_6_9·b_6_10 − b_4_6·a_3_4·a_5_8 + b_4_6·a_1_1·a_7_14 + b_2_2·a_3_4·a_7_14
       + b_2_2·b_4_6·a_1_1·a_5_8 − b_2_22·a_3_4·a_5_8 + b_2_22·a_3_2·a_5_8
       − b_2_2·c_6_11·a_1_1·a_3_4 − b_2_2·c_6_11·a_1_1·a_3_2
  78. a_5_8·a_7_14 + c_6_11·a_3_2·a_3_4 + c_6_11·a_1_1·a_5_7
  79. b_6_10·a_7_14 + b_4_62·a_5_8 + b_2_2·b_4_6·a_7_14 − b_2_2·b_4_6·c_6_11·a_1_1
       + b_2_22·c_6_11·a_3_4 + b_2_22·c_6_11·a_3_2
  80. a_6_9·a_7_14

About the group Ring generators Ring relations Completion information Restriction maps Back to groups of order 81

Data used for Benson′s test

  • Benson′s completion test succeeded in degree 13.
  • 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_11, a Duflot regular element of degree 6
    2.  − b_4_63 + b_2_22·b_4_62 + b_2_26 + b_2_06, an element of degree 12
    3.  − b_2_22·b_4_63 + b_2_24·b_4_62, an element of degree 16
  • The Raw Filter Degree Type of that HSOP is [-1, -1, 15, 31].
  • The filter degree type of any filter regular HSOP is [-1, -2, -3, -3].
  • We found that there exists some filter regular HSOP formed by the first term of the above HSOP, together with 2 elements of degree 4.

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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. a_2_1 → 0, an element of degree 2
  4. b_2_0 → 0, an element of degree 2
  5. b_2_2 → 0, an element of degree 2
  6. a_3_2 → 0, an element of degree 3
  7. a_3_3 → 0, an element of degree 3
  8. a_3_4 → 0, an element of degree 3
  9. a_4_5 → 0, an element of degree 4
  10. b_4_6 → 0, an element of degree 4
  11. a_5_7 → 0, an element of degree 5
  12. a_5_8 → 0, an element of degree 5
  13. a_6_9 → 0, an element of degree 6
  14. b_6_10 → 0, an element of degree 6
  15. c_6_11 → c_2_03, an element of degree 6
  16. a_7_14 → 0, an element of degree 7

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_1 → 0, an element of degree 1
  3. a_2_1 → 0, an element of degree 2
  4. b_2_0 → c_2_2, an element of degree 2
  5. b_2_2 → 0, an element of degree 2
  6. a_3_2 → 0, 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. a_3_4 → 0, an element of degree 3
  9. a_4_5 → 0, an element of degree 4
  10. b_4_6 → 0, an element of degree 4
  11. a_5_7 → 0, an element of degree 5
  12. a_5_8 → 0, an element of degree 5
  13. a_6_9 → 0, an element of degree 6
  14. b_6_10 → 0, an element of degree 6
  15. c_6_11 →  − c_2_1·c_2_22 + c_2_13, an element of degree 6
  16. a_7_14 → 0, an element of degree 7

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 → a_1_1, an element of degree 1
  3. a_2_1 →  − a_1_1·a_1_2, an element of degree 2
  4. b_2_0 → 0, an element of degree 2
  5. b_2_2 → c_2_4, an element of degree 2
  6. a_3_2 → c_2_5·a_1_1 − c_2_4·a_1_2, an element of degree 3
  7. a_3_3 →  − a_1_0·a_1_1·a_1_2, an element of degree 3
  8. a_3_4 →  − c_2_5·a_1_2 − c_2_5·a_1_1 − c_2_4·a_1_2 + c_2_4·a_1_0 + c_2_3·a_1_1, an element of degree 3
  9. a_4_5 →  − c_2_5·a_1_0·a_1_1 + c_2_4·a_1_0·a_1_2 − c_2_3·a_1_1·a_1_2, an element of degree 4
  10. b_4_6 →  − c_2_52 + c_2_4·c_2_5 − c_2_3·c_2_4, an element of degree 4
  11. a_5_7 → c_2_52·a_1_2 − c_2_4·c_2_5·a_1_2 − c_2_3·c_2_5·a_1_1 + c_2_3·c_2_4·a_1_2
       − c_2_3·c_2_4·a_1_1, an element of degree 5
  12. a_5_8 →  − c_2_52·a_1_0 + c_2_4·c_2_5·a_1_0 + c_2_3·c_2_5·a_1_2 + c_2_3·c_2_5·a_1_1
       + c_2_3·c_2_4·a_1_2 − c_2_3·c_2_4·a_1_0 + c_2_32·a_1_1, an element of degree 5
  13. a_6_9 →  − c_2_52·a_1_0·a_1_2 + c_2_4·c_2_5·a_1_0·a_1_2 + c_2_3·c_2_5·a_1_1·a_1_2
       + c_2_3·c_2_5·a_1_0·a_1_1 − c_2_3·c_2_4·a_1_1·a_1_2 − c_2_3·c_2_4·a_1_0·a_1_2
       + c_2_3·c_2_4·a_1_0·a_1_1 − c_2_32·a_1_1·a_1_2, an element of degree 6
  14. b_6_10 → c_2_53 − c_2_4·c_2_52 − c_2_3·c_2_42, an element of degree 6
  15. c_6_11 →  − c_2_3·c_2_52 + c_2_3·c_2_4·c_2_5 + c_2_32·c_2_4 + c_2_33, an element of degree 6
  16. a_7_14 → c_2_53·a_1_0 − c_2_4·c_2_52·a_1_0 − c_2_3·c_2_52·a_1_2 − c_2_3·c_2_52·a_1_1
       − c_2_3·c_2_4·c_2_5·a_1_2 + c_2_3·c_2_4·c_2_5·a_1_1 − c_2_3·c_2_42·a_1_2
       − c_2_3·c_2_42·a_1_0 − c_2_32·c_2_5·a_1_1 + c_2_32·c_2_4·a_1_2 + c_2_32·c_2_4·a_1_1, an element of degree 7

About the group Ring generators Ring relations Completion information Restriction maps Back to groups of order 81


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