Alphabeta Math
TheoremStatement: Literature-sourcedProof: AI-adaptedprecheck passaudited 2026-08-11
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Every finite permutation is a product of transpositions, so the transpositions generate Sn

Statement

Every permutation of a finite set is a product of transpositions. Consequently, for every natural n, the transpositions in Sn=Sym⁡(n) generate Sn. The identity, including the only permutations in S0 and S1, is represented by the empty product.

Facts & Assumptions

Given: A finite set X and a permutation σ∈Sym⁡(X), with the right-hand factor in a product acting first.

[L1]

Every finite permutation is a product of pairwise disjoint cycles, with the identity represented by the empty product (Every permutation of a finite set is a product of pairwise disjoint cycles, uniquely up to reordering and cyclic rotation).

[L2]

The subgroup generated by a subset is the smallest subgroup containing that subset (The subgroup ⟨S⟩ generated by a subset, the cyclic subgroup ⟨g⟩, and cyclic groups).

Proof

technique · direct
1.1givenL1

For k≥2, pointwise evaluation gives (a0 a1 … ak−1)=(a0 ak−1)⋯(a0 a2)(a0 a1): the rightmost factor sends a0 to a1, each ai to ai+1, and the leftmost factor sends ak−1 back to a0, while all other points are fixed.

2.1step 1.1L1

Replace each cycle in the decomposition supplied by [L1] with the factorisation in step 1.1 and concatenate the resulting finite lists. This expresses σ as a product of transpositions.

3.1step 2.1L1L2∎

If σ is the identity, the decomposition and the resulting list are empty. Thus the conclusion includes n=0 and n=1, and every element of Sn lies in the smallest subgroup containing all transpositions, which by [L2] says that the transpositions generate Sn.

Depends on

Dependency tree · 2 levels

Sources