
≡
S
ν
0
ν
1
S
0
⊆ S
S
0
(
S, ν
0
)
(S, ν
1
)
ν
S f
f(0) = 0
f(k + 1) = min{z | νz /∈ {νf(0), . . . , νf(k)}}.
f S
ν
x y ν(x) ν(y)
f(x)
ν
∗
(x) = νf(x) ν
∗
S
S
ν
∗
(k + 1) = νf(k + 1) /∈ {ν
∗
(0), . . . , ν
∗
(k)}
ν
∗
(k + 1) ν
∗
(0), . . . , ν
∗
(k)
ν
S s ∈ S m(s) = min{i | ν(i) = s}
M = {m(s) | s ∈ S} = {a
0
< a
1
< a
2
< . . .}.