identity permutation e a(1)a(2)…a(n) inverse permutation of o o 2 a1(1)a(2)…a(n)        =         =         = − − − − − σ (1) σ (2) σ (n) 1 2 n σ 1 2 n σ(1) σ(2) σ(n) σ 1 2 n 1 2 n e 1 1 1 1 1       inverse permutation of  identity permutation