Permutation sign and alternating group
The parity of the number of transpositions in a permutation factorization is invariant.
Key knowledge
The parity of the number of transpositions in a permutation factorization is invariant. It defines the homomorphism sgn:Sₙ→{1,−1}; sgn(στ)=sgn(σ)sgn(τ). Its kernel Aₙ comprises even permutations, is normal and has n!/2 elements. A k-cycle has sign (−1)ᵏ⁻¹.
Conditions and scope
- n≥2 for surjectivity and the stated half-order.
- Parity is independent of the chosen transposition factorization; cycle lengths do not determine a unique written ordering.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Definitions 11.1, Lemmas 11.2/11.5 and Definition-Lemma 11.6; cycle sign uses k−1 transpositions. Source's later simplicity statement is not adopted.
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Entry details
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- university-core.1
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- University core expansion