Definition:Barrier

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Definition

A complex function $\varphi \in \map \C {\overline \Omega}$ is a barrier for $\Omega$ at $z \in \partial \Omega$ if and only if:

$\varphi$ is subharmonic
$\map \varphi z = 0$
$\varphi < 0$ on $\partial \Omega \setminus \set z$











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