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Group theory and generalizations Proof

Proof that the symmetric group is generated by transpositions

Builds on Symmetric groupTranspositionSubgroup generated by a subsetSubgroupDecomposition of a permutation into transpositions

Proof

  1. Let n≥2n \ge 2, let SnS_n be the symmetric group, and let TT be the set of all transpositions in SnS_n.
  2. By definition, the subgroup generated by TT is the intersection ⟨T⟩\langle T \rangle of all subgroups of SnS_n that contain TT. In particular, ⟨T⟩⊆Sn\langle T \rangle \subseteq S_n.
  3. Let UU be a subgroup of SnS_n with T⊆UT \subseteq U. A subgroup is closed under products, so by induction on the number of factors, UU contains each product of elements of TT.
  4. By the decomposition into transpositions, each σ∈Sn\sigma \in S_n is such a product. So U=SnU = S_n.
  5. By steps 3 and 4, the only subgroup of SnS_n that contains TT is SnS_n itself. Hence ⟨T⟩=Sn\langle T \rangle = S_n.

Idea

Any subgroup that contains all transpositions contains all their products. Every permutation is such a product, so that subgroup is the whole group.

Reading path

To understand this page from the ground up, read these 75 pages in order. The foundations come first. The path takes the proofs Proof of the decomposition of a permutation into transpositions, Proof of the commutativity of addition by induction, Proof that equivalence classes form a partition, Proof that disjoint cycles commute, Proof of strong induction from ordinary induction, Proof of the laws of exponents in a group, Proof that an intersection of subgroups is a subgroup, Proof of the decomposition of a permutation into disjoint cycles, Proof of the well-ordering principle from strong induction, Proof of the division algorithm, Proof of the uniqueness of inverses, Proof of the subgroup criterion.

  1. Binary operation definition
  2. Cycle notation concept
  3. Definition by recursion concept
  4. Divisibility definition
  5. Element definition
  6. Group concept
  7. Mathematical induction concept
  8. Natural numbers object
  9. Peano axioms concept
  10. Proposition concept
  11. Identity element definition
  12. Set definition
  13. Subgroup definition
  14. Symmetric group definition
  15. Successor function definition
  16. Conjunction definition
  17. Disjunction definition
  18. Implication definition
  19. Predicate definition
  20. Inverse element definition
  21. Empty set object
  22. Family of sets definition
  23. Ordered pair definition
  24. Transposition definition
  25. Intersection definition
  26. Proof that an intersection of subgroups is a subgroup proof
  27. Union definition
  28. Addition of natural numbers definition
  29. Set-builder notation concept
  30. Biconditional definition
  31. The successor function is injective statement
  32. Zero is not a successor statement
  33. Existential quantifier definition
  34. Universal quantifier definition
  35. Proof of the uniqueness of inverses proof
  36. Cartesian product definition
  37. Disjoint sets definition
  38. Proof of the commutativity of addition by induction proof
  39. Subset definition
  40. Axiom of extensionality statement
  41. Union of a family of sets definition
  42. Order on the natural numbers definition
  43. Uniqueness quantifier definition
  44. Uniqueness of inverses statement
  45. Binary relation definition
  46. Partition of a set definition
  47. Commutativity of addition statement
  48. Proof of strong induction from ordinary induction proof
  49. Reflexive relation definition
  50. Symmetric relation definition
  51. Transitive relation definition
  52. Proof of the subgroup criterion proof
  53. Proof of the laws of exponents in a group proof
  54. Function definition
  55. Strong induction statement
  56. Equivalence relation definition
  57. Subgroup criterion statement
  58. Laws of exponents in a group statement
  59. Injective function definition
  60. Proof of the well-ordering principle from strong induction proof
  61. Proof that disjoint cycles commute proof
  62. Intersection of subgroups is a subgroup statement
  63. Equivalence class definition
  64. Well-ordering principle statement
  65. Disjoint cycles commute statement
  66. Subgroup generated by a subset definition
  67. Proof that equivalence classes form a partition proof
  68. Proof of the division algorithm proof
  69. Equivalence classes form a partition statement
  70. Division algorithm statement
  71. Proof of the decomposition of a permutation into disjoint cycles proof
  72. Decomposition of a permutation into disjoint cycles statement
  73. Proof of the decomposition of a permutation into transpositions proof
  74. Decomposition of a permutation into transpositions statement
  75. Proof that the symmetric group is generated by transpositions proof

Where this leads

248 pages build on this one.

Further reading

  1. Web https://en.wikipedia.org/wiki/Symmetric_group, Generators and relations
About this page
Tag36FRFTA090
URIm2://36FRFTA090
Kindproof
WritingW0 stub
MSC20B30
ProvesThe symmetric group is generated by transpositions
UsesSymmetric group, Transposition, Subgroup generated by a subset, Subgroup, Decomposition of a permutation into transpositions
Changed4 November 2026

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