12 1-2 2-3 13 1/2 1/2 0 0 reducible 1/3 2/3 0 0 0 3/4 1/4 4 0 0 1/4 3/4 34 34 14 0.4 0.6 0 0 p20 0.4 0.6 0 0 ≈ 0 0 0.5 0.5 0 0 0.5 0.5P = ￾ ⇧ ⇧ ⇤ 1/2 1/20 0 1/3 2/30 0 0 03/4 1/4 0 01/4 3/4 ⇥ ⌃ ⌃ ⌅ P20 ￾ ￾ ⇧ ⇧ ⇤ 0.4 0.60 0 0.4 0.60 0 0 00.5 0.5 0 00.5 0.5 ⇥ ⌃ ⌃ ⌅ 1 2 1 2 1 3 2 3 3 4 1 4 3 4 1 4 reducible