X_a

X_b

X_aa

X_ab

X_ba

X_bb

X_aaa

X_aab

X_aba

X_abb

X_baa

X_bab

X_bba

X_bbb

(11, 33)

(55, 77)

(15, 37)

(51, 73)

(13, 31)

(57, 75)

(17, 35)

(53, 75)

(22, 44)

(66, 88)

(26, 48)

(62, 84)

(24, 42)

(68, 86)

(28, 46)

(62, 84)

(12, 34)

(56, 78)

(16, 38)

(52, 74)

(14, 32)

(58, 76)

(18, 36)

(54, 72)

(21, 43)

(65, 87)

(25, 47)

(61, 83)

(23, 41)

(67, 85)

(27, 45)

(63, 81)