Pome

Theorem 10.31.56AC45579AB2E

Theorem 10.31.5.6AC45579AB2E Suppose $u_ j\in \mathcal E_\varphi $, $u_ j\to u\in \mathrm{PSH}(X,\theta )$ in $L^1(X)$, and $\mu _{u_ j}\leq \nu $ for one finite non-pluripolar measure $\nu $. Then there is a subsequence with

\[ h=P_\theta \left(\inf _ j u_ j\right)\in \mathcal E_\varphi . \]

Moreover, for the original sequence,

\[ u\in \mathcal E_\varphi ,\qquad u_ j\longrightarrow u\text{ in capacity},\qquad \mu _{u_ j}\rightharpoonup \mu _ u\leq \nu . \]

Proof. We follow the proofs of lemma 15.37.13, theorem 15.37.19 and check their ingredients in the present background. The envelope identity and Hartogs' lemma give $u_ j\leq \varphi +C$. Finite rooftops and stretching envelopes of members of $\mathcal E_\varphi $ stay in $\mathcal E_\varphi $ by proposition 16.28.64, lemma 16.28.63, and their masses are at least $\ell $ by (10.31.1). These facts replace the corresponding ones for semipositive backgrounds.

After a common translation, assume $u_ j,u\leq \varphi \leq 0$. Using lemma 5.44.2, extract once and for all a subsequence along which $u_ j\to u$ almost everywhere for smooth volume and

\[ I_ j:=\int _ X|\mathrm{e}^{u_ j}-\mathrm{e}^ u|\, \mu _{u_ j}\leq 2^{-j}. \]

For $p_{j,N}=P_\theta (u_ j,\ldots ,u_ N)$, partitioning the contact set according to the first obstacle touched gives

C0EFA39C2570 10.31.6
\begin{equation} \mu _{p_{j,N}}\leq \nu ,\qquad \int _ X|\mathrm{e}^{p_{j,N}}-\mathrm{e}^ u|\, \mu _{p_{j,N}}\leq 2^{1-j}. \end{equation}

In the proof of the extraction lemma, replace $\kappa $ by $\ell $. For each fixed $B\geq 1$, the stretched rooftops $r_{j,N}=Q_ B(p_{j,N},\varphi )$ satisfy

\[ \ell \leq \mu _{r_{j,N}}(X),\qquad \mu _{r_{j,N}}\leq B^ n\nu . \]

The exponential test (15.37.15) therefore bounds $\sup _ Xr_{j,N}$ from below, independently of $N$, once $j$ is sufficiently large. The construction combining the tail with the finitely many earlier terms, with $B=2b$, uses only convex combinations and finite rooftops that are not identically $-\infty $. It provides every defining competitor for

\[ h=P_\theta (\inf _ j u_ j)\in \mathcal E_\varphi . \]

Since $h\leq u\leq \varphi $, upward stability gives $u\in \mathcal E_\varphi $.

For the continuity statements, put $p_ j=P_\theta (\inf _{k\geq j}u_ k)$ and $p=(\lim _ jp_ j)^*$. The monotone limits $p_{j,N}\downarrow p_ j$ and $p_ j\uparrow p$ have the common lower bound $h\not\equiv -\infty $, so they hold in capacity by lemma 5.29.19. All the limits lie in $\mathcal E_\varphi $, and $p\leq u$. Applying lemma 13.14.8 twice to (10.31.6) gives

\[ \int _ X|\mathrm{e}^ p-\mathrm{e}^ u|\, \mu _ p=0. \]

Hence $\mu _ p(\{ p<u\} )=0$, and zero domination (theorem 13.19.1 with coefficient zero) gives $p=u$. The upper envelopes $(\sup _{k\geq j}u_ k)^*$ decrease to $u$ by Hartogs' lemma, and squeezing the $u_ j$ between them and $p_ j$ proves convergence in capacity.

Finally, the fixed finite dominating measure gives

\[ \mu _{u_ j}(\{ u_ j\leq -T\} )\leq \nu (\{ h\leq -T\} )\longrightarrow 0 \]

uniformly in $j$, and theorem 13.15.23 proves weak convergence to $\mu _ u\leq \nu $. Starting with an arbitrary subsequence, we obtain a further subsequence with both convergences and the same limit. Hence the conclusions hold for the original sequence. $\square$

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