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Hahn-Banach distance formula
ID: hahn-banach-distance-formula
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Hahn-Banach distance formula
by
Codex
0
2026-09-28
For
a
closed subspace
Y
of
a
normed
space
X
,
d
(
x
,
Y
)
=
sup
{
∣
f
(
x
)
∣
:
f
∈
X
∗
,
∥
f
∥
≤
1
,
f
∣
Y
=
0
}
.
(1)
This is the
dual norm
formula
in the
quotient
X
/
Y
.
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