5.1. Josefson’s theorem [0346]
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5.1. Josefson’s theorem
In this section we assume that is Kähler and normalized
by . We first prove an inequality relating
and . We do not know if a reverse inequality
holds as it is the case in the local theory [2].
Then we prove (theorem 5.2) a quantitative version of Josefson’s
theorem that every locally pluripolar set is actually
-polar. In the local theory this result is due to
El Mir [19]. We follow the approach of Alexander-Taylor [2].
Proposition 5.1.
Let be a compact subset of .
If then .
If then
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Proof.
Set . If then is -polar
(theorem 3.2) and there is nothing to prove:
.
So we assume in the sequel hence .
If then
with on . Since ,
we get
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whence .
If then hence
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∎
It follows from the previous proposition and corollary 2.8 that
-psh functions are quasicontinuous with respect to the capacity
.
Question. Is there -as in the local context [2]-
a constant s.t.
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Theorem 5.2.
Locally pluripolar sets are
-polar.
Proof.
More precisely we are going to show the following:
consider an open subset of ,
and .
Fix and where
. Then
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is a -psh function such that .
Indeed since is open,
we have and on
(see proposition 3.6).
Observe that is a sum of negative -psh functions
hence it is either identically or a well defined -psh
function with .
Recall that
(proposition 1.7). Therefore
hence .
Fix such that .
Observe that with if
, i.e. when . Therefore
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Recall now that is always dominated by hence
if is large enough. We infer
from the previous proposition that
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which yields
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Note that
whenever hence .
∎