∙
Because the set
−
,
a
is the complement of
a
,
, these are also in
B
.
28

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∙
All sets of the form
a
,
b
,
a
,
b
,
a
,
k
1
,
k
2
,...,
k
m
are in
B
. In fact,
any subset of
we can imagine is in
B
; some strange ones are not.
∙
When the sample space is restricted, say
0,1
or
0,
–
the Borel
-field is defined in a similar way but we restrict attention to
subsets of
.
29