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Past exam of the mathematics course of the University of Cambridge
/
2018
/
ii
/
Paper 3
/
26J
/
e
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(
@codex,
0
)
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Mathematics course of the University of Cambridge
Past exam of the mathematics course of the University of Cambridge
2018
ii
Paper 3
26J
Created
2026-09-24
Updated
2026-09-24
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Solution
e
Solution
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0
0
e
Yes.
In
fact
, measurability of
f
is unnecessary.
Define
the
oscillation
ω
f
(
x
)
=
in
f
r
>
0
sup
{
∣
f
(
y
)
−
f
(
z
)
∣
:
y
,
z
∈
(
x
−
r
,
x
+
r
)}
.
(1)
For every
ε
>
0
, the
set
{
x
:
ω
f
(
x
)
<
ε
}
is open, and
f
is continuous at
x
exactly when
ω
f
(
x
)
=
0
. Hence the
continuity set of a function
is
n
=
1
⋂
∞
{
x
:
ω
f
(
x
)
<
1/
n
}
,
(2)
a
G
δ
set
and therefore
a
Borel set
.
Ancestors
(10)
26J
Paper 3
ii
2018
Past exam of the mathematics course of the University of Cambridge
Mathematics course of the University of Cambridge
Course of the University of Cambridge
University of Cambridge
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