ABSTRACT
THEOREM 11.1 For each set X, the operation of composition on the set, S(X), of permutations of X has the following properties.
a. For all σ, τ ∈ S(X), στ ∈ S(X). b. For all σ ∈ S(X), σιX = σ = ιXσ. c. For all σ ∈ S(X), σσ-1 = ιX = σ-1σ. d. For all σ, τ ,ρ ∈ S(X), (στ) ρ = σ (τρ).
