A

x

y

B

y ˜

x ˜

z

C = B 1 y 1 z y B

A 1 = τ 2

τ 2

σ 1

τ σ 2 τ 3 σ 3 = B 1

σ 1

τ 2

ω 2 1

C 1 = B 1 1 σ ω 2 1 σ 1 B 1

A 2 = empty

τ 2

σ 1

τ 1 σ 2 τ 3 σ 3 = B 2

σ 1

τ 2

ω 2 1

C 2 = B 2 1 σ ω 2 1 σ 1 B 2

A 3 = σ 1 τ 2

τ 1

σ 2

τ 3 σ 3 = B 3

σ 2

τ 1

ω 5

C 3 = B 3 1 σ 2 ω 5 σ 2 B 3

A 4 = σ 1 τ 1

τ 1

σ 2

τ 2 σ 3 = B 4

σ 2

τ 1

ω 4

C 4 = B 4 1 σ 2 ω 4 σ 2 B 4

A 5 = σ 1

τ 1

σ 2

τ σ 3 = B 5

σ 2

τ 1

ω 5

C 5 = B 5 1 σ 2 ω 5 σ 2 B 5