α β γ
A B
A B p q A
A
i
A
i B
j
B j A
A B
B A = A
1
∪ A
c
1
B
c
1
A
2
∪ . . .
B = A
c
1
B
1
∪ A
c
1
B
c
1
A
c
2
B
2
∪ . . .
A
1
, B
1
, A
2
, B
2
. . .
P
(A) = p + (1 − p)(1 − q)p + (1 − p)(1 − q)(1 − p)(1 − q)p + ··· =
= p(1 + (1 − p)(1 − q) + (1 − p)
2
(1 − q)
2
+ ···) =
p
1 − (1 − p)(1 − q)
.
P
(B) = (1−p)q+(1−p)(1−q)(1−p)q+(1−p)(1−q)(1−p)(1−q)(1−p)q+···
= (1 −p)q(1 + (1 −p)(1 −q) + (1 −p)
2
(1 −q)
2
+ ···) =
(1 − p)q
1 − (1 − p)(1 − q)
.
P
(A) +
P
(B) =
p+(1−q)p
1−(1−p)(1−q)
=
p+q−pq
p+q−pq
= 1
0
a b
3 5 2
1