×
s
s+u
s+t+u+v
s+u
s+t+u+v
s
=
P(A|B)
×
=
P(B)
P(B) P(A|B)
u
v
s
t
A
notA
B
notB
u
v
s
t
B
notB
×
u
v
s
t
B
notB
=
A
A