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4 Existence and uniqueness of the solutions. [029E]

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4 Existence and uniqueness of the solutions.

Theorem 6

. Let XX be a compact Kähler manifold of complex dimension nn, let Ω>0\Omega>0 be a smooth volume form, let θ\theta be a continuous closed positive (1,1)(1,1)-form such that {θn=0}\{\theta^{n}=0\} is a set of measure 00, let γ\gamma be a closed positive (1,1)(1,1)-current with continuous local potentials such that γ≥η​θ\gamma\geq\eta\,\theta, η>0\eta>0. Let also f∈L​logn+δ​L​(X)f\in L\log^{n+\delta}L(X), δ>0\delta>0 such that ∫Xγn=∫Xf​Ω\int_{X}\gamma^{n}=\int_{X}f\,\Omega and λ≥0\lambda\geq 0 be a real number. Then there exists a unique solution ψ∈𝒫^γ\psi\in\hat{\cal P}_{\gamma} of the degenerate complex Monge-Ampère equation

(γ+i​∂∂¯​ψ)n=f​eλ​ψ​Ω,(\gamma+i\partial\bar{\partial}\psi)^{n}=f\,e^{\lambda\,\psi}\Omega\,,

which in the case λ=0\lambda=0 is normalized by 0=maxX⁡ψ0=\max_{X}\psi. The solution is continuous and satisfies the C0C^{0}-estimate ‖ψ‖C0​(X)≤C⁡(δ,γ,Ω)​Iδ​(f)nδ+1\|\psi\|_{C^{0}(X)}\leq C(\delta,\gamma,\Omega)\,I_{\delta}(f)^{\frac{n}{\delta}}+1, with

Iδ​(f):={γ}−n​∫Xf​logn+δ⁡(e+{γ}−n​f)​Ω.I_{\delta}(f):=\{\gamma\}^{-n}\int\limits_{X}f\log^{n+\delta}\left(e+\{\gamma\}^{-n}f\right)\Omega\,.

Moreover the constant C⁡(δ,γ,Ω)>0C(\delta,\gamma,\Omega)>0 stays bounded for perturbations of γ≥0\gamma\geq 0 as in the statement (C) of theorem 3.

Proof. Let ω>0\omega>0 be a Kähler metric and write γ=θ+i​∂∂¯​u\gamma=\theta+i\partial\bar{\partial}u whith θ\theta smoth and uu continuous. There exist a sequence γj=θ+i​∂∂¯​uj\gamma_{j}=\theta+i\partial\bar{\partial}u_{j}, whith uj∈C∞​(X)u_{j}\in C^{\infty}(X), such that uj↓uu_{j}\downarrow u uniformly and 0<γj+εj​ω0<\gamma_{j}+\varepsilon_{j}\omega whith 0<εj↓00<\varepsilon_{j}\downarrow 0. We consider also a regularizing family (fj)j⊂C∞​(X)(f_{j})_{j}\subset C^{\infty}(X), fj>0f_{j}>0 of ff in L​logn+δ​L​(X)L\log^{n+\delta}L(X). We can assume

∫X(γj+εj​ω)n=∫Xfj​Ω,\int\limits_{X}(\gamma_{j}+\varepsilon_{j}\omega)^{n}=\int\limits_{X}f_{j}\,\Omega\,,

otherwise we multiply fjf_{j} by a constant cj>0c_{j}>0 which converges to 11 by the normalising condition ∫Xγn=∫Xf​Ω\int_{X}\gamma^{n}=\int_{X}f\,\Omega. We distinguish two cases.

Case λ=0\lambda=0. By Yau’s solution of the Calabi conjecture there exists a unique family (ψj)j(\psi_{j})_{j}, ψj∈𝒫γj+εj​ω0\psi_{j}\in{\cal P}^{0}_{\gamma_{j}+\varepsilon_{j}\omega} of smooth solutions of the complex Monge-Ampère equations

(γj+εj​ω+i​∂∂¯​ψj)n=fj​Ω.(\gamma_{j}+\varepsilon_{j}\omega+i\partial\bar{\partial}\psi_{j})^{n}=f_{j}\,\Omega\,.

The hypothesis (C1) and (C2a) of statement (C) of theorem 3 are obviously satisfied for the family (γj+εj)j(\gamma_{j}+\varepsilon_{j})_{j}. We deduce that the constant C1=C1​(δ,γj+εj​ω,Ω)>0C_{1}=C_{1}(\delta\,,\,\gamma_{j}+\varepsilon_{j}\omega\,,\,\Omega)>0 in the statement of theorem 3,A does not blow up as j→+∞j\rightarrow+\infty. Moreover the uniform estimate

‖fj‖L​logn+δ​L​(X)≤C′​‖f‖L​logn+δ​L​(X)=:K,\displaystyle\|f_{j}\|_{L\log^{n+\delta}L(X)}\leq C^{\prime}\|f\|_{L\log^{n+\delta}L(X)}=:K\,, (4.1)

holds for all jj. (See [Ra-Re] page 364 or [Iw-Ma], theorem 4.12.2, page 79.) Thus by theorem 3, A we obtain the uniform estimate ‖ψj‖C0​(X)≤C\|\psi_{j}\|_{C^{0}(X)}\leq C. On the other hand we have a priori a uniform estimate ∫X−ψjΩ≤C′\int_{X}-\psi_{j}\,\Omega\leq C^{\prime} since the local potentials of the family (γj+εj)j(\gamma_{j}+\varepsilon_{j})_{j} stay uniformly bounded. Thus, by elementary properties of plurisubharmonic functions, (see [Dem1], chapter 1) there exists a L1L^{1}-convergent subsequence (ψj)j(\psi_{j})_{j} (which by abuse of notations we denote in the same way). We can apply theorem 3, B to the complex Monge-Ampère equation in consideration since we dispose of the estimate (4.1) and the constant C2=C2​(δ,γj+εj​ω,Ω,K)>0C_{2}=C_{2}(\delta\,,\,\gamma_{j}+\varepsilon_{j}\omega\,,\,\Omega,K)>0 in the relative statement is uniformly bounded in jj thanks to the same considerations concerning the constant C1C_{1}. We infer that the sequence (ψj)j(\psi_{j})_{j} is a Cauchy sequence in the C0C^{0}-topology, thus convergent to some ψ∈𝒫γ∩C0​(X)\psi\in{\cal P}_{\gamma}\cap C^{0}(X). This implies the convergence of the weak limits

(γ+i​∂∂¯​ψ)n=limj→+∞(γj+εj​ω+i​∂∂¯​ψj)n=limj→+∞fj​Ω=f​Ω,(\gamma+i\partial\bar{\partial}\psi)^{n}=\lim_{j\rightarrow+\infty}(\gamma_{j}+\varepsilon_{j}\omega+i\partial\bar{\partial}\psi_{j})^{n}=\lim_{j\rightarrow+\infty}f_{j}\,\Omega=f\,\Omega\,,

thus ψ\psi is the required solution of our degenerate complex Monge-Ampère equation. We normalise the solution ψ\psi whith the condition maxX⁡ψ=0\max_{X}\psi=0. We prove now the uniqueness of the solutions in the case λ=0\lambda=0. Let φ∈𝒫^γ0\varphi\in\hat{\cal P}^{0}_{\gamma} be another solution. Then the identity γφn=γψn\gamma_{\varphi}^{n}=\gamma_{\psi}^{n} implies φ∈𝒫ˇγ0\varphi\in\check{\cal P}^{0}_{\gamma} by claim 2 in the proof of theorem 5. Let φε\varphi_{\varepsilon}, ψε\psi_{\varepsilon} be as in the statement of corollary 3 and set u:=ψ−φu:=\psi-\varphi, uε:=ψε−φεu_{\varepsilon}:=\psi_{\varepsilon}-\varphi_{\varepsilon}. Let us also recall the formula

αk−βk=(α−β)∧∑l=0k−1αl∧βk−l−1.\alpha^{k}-\beta^{k}=(\alpha-\beta)\wedge\sum_{l=0}^{k-1}\alpha^{l}\wedge\beta^{k-l-1}\,.

From there we deduce

0\displaystyle 0 =\displaystyle= ∫X−u(γψn−γφn)=limε→0+∫X−uε(γψn−γφn)\displaystyle\int\limits_{X}-u(\gamma^{n}_{\psi}-\gamma^{n}_{\varphi})=\lim_{\varepsilon\rightarrow 0^{+}}\int\limits_{X}-u_{\varepsilon}(\gamma^{n}_{\psi}-\gamma^{n}_{\varphi}) (4.2)
=\displaystyle= limε→0+∑l=0n−1∫X−uεi∂∂¯u∧γlψ∧γn−l−1φ\displaystyle\lim_{\varepsilon\rightarrow 0^{+}}\,\sum_{l=0}^{n-1}\,\int\limits_{X}-u_{\varepsilon}\,i\partial\bar{\partial}u\wedge\gamma^{l}_{\psi}\wedge\gamma^{n-l-1}_{\varphi}
=\displaystyle= limε→0+∑l=0n−1∫Xi​∂uε∧∂¯​u∧γψl∧γφn−l−1\displaystyle\lim_{\varepsilon\rightarrow 0^{+}}\,\sum_{l=0}^{n-1}\,\int\limits_{X}i\partial u_{\varepsilon}\wedge\bar{\partial}u\wedge\gamma^{l}_{\psi}\wedge\gamma^{n-l-1}_{\varphi}
=\displaystyle= ∑l=0n−1∫Xi​∂u∧∂¯​u∧γψl∧γφn−l−1=:I,\displaystyle\sum_{l=0}^{n-1}\,\int\limits_{X}i\partial u\wedge\bar{\partial}u\wedge\gamma^{l}_{\psi}\wedge\gamma^{n-l-1}_{\varphi}=:I\,,

since ∂uε→∂u\partial u_{\varepsilon}\rightarrow\partial u in L2​(X,γψl∧γφn−l−1)L^{2}(X,\gamma^{l}_{\psi}\wedge\gamma^{n-l-1}_{\varphi}) by corollary 3. Inspired by an idea of S. Blocki [Blo1], we will prove by induction on k=0,…,n−1k=0,...,n-1 that

∫Xi​∂u∧∂¯​u∧γψr∧γφs∧γk=0\displaystyle\int\limits_{X}i\partial u\wedge\bar{\partial}u\wedge\gamma^{r}_{\psi}\wedge\gamma^{s}_{\varphi}\wedge\gamma^{k}=0 (4.3)

for all r,s≥0r,s\geq 0, r+s=n−k−1r+s=n-k-1. For k=0k=0 this follows from (4.2). So we assume (4.3) for k−1k-1 and we prove it for kk. In fact consider the identity

γk=γψk−i​∂∂¯​ψ∧∑l=0k−1γψl∧γk−l−1and set Ξ:=γψr∧γφs∧∑l=0k−1γψl∧γk−l−1.\gamma^{k}=\gamma^{k}_{\psi}-i\partial\bar{\partial}\psi\wedge\sum_{l=0}^{k-1}\gamma^{l}_{\psi}\wedge\gamma^{k-l-1}\quad\mbox{and set }\quad\Xi:=\gamma^{r}_{\psi}\wedge\gamma^{s}_{\varphi}\wedge\sum_{l=0}^{k-1}\gamma^{l}_{\psi}\wedge\gamma^{k-l-1}\,.

By applying several times corollary 3 and by integrating by parts we derive

∫Xi​∂u∧∂¯​u∧γψr∧γφs∧γk=limε→0+∫Xi​∂uε∧∂¯​u∧γψr∧γφs∧γk\displaystyle\int\limits_{X}i\partial u\wedge\bar{\partial}u\wedge\gamma^{r}_{\psi}\wedge\gamma^{s}_{\varphi}\wedge\gamma^{k}\;=\;\lim_{\varepsilon\rightarrow 0^{+}}\int\limits_{X}i\partial u_{\varepsilon}\wedge\bar{\partial}u\wedge\gamma^{r}_{\psi}\wedge\gamma^{s}_{\varphi}\wedge\gamma^{k}
=\displaystyle= limε→0+[∫Xi​∂uε∧∂¯​(u​γψr+k∧γφs)−∫Xi​∂uε∧∂¯​(u​i​∂∂¯​ψ∧Ξ)]\displaystyle\lim_{\varepsilon\rightarrow 0^{+}}\,\left[\;\int\limits_{X}i\partial u_{\varepsilon}\wedge\bar{\partial}(u\gamma^{r+k}_{\psi}\wedge\gamma^{s}_{\varphi})\;-\;\int\limits_{X}i\partial u_{\varepsilon}\wedge\bar{\partial}(u\,i\partial\bar{\partial}\psi\wedge\Xi)\;\right]
=\displaystyle= limε→0+[∫Xi​∂uε∧∂¯​u∧γψr+k∧γφs+∫Xuε​i​∂∂¯​u∧i​∂∂¯​ψ∧Ξ]\displaystyle\lim_{\varepsilon\rightarrow 0^{+}}\,\left[\;\int\limits_{X}i\partial u_{\varepsilon}\wedge\bar{\partial}u\wedge\gamma^{r+k}_{\psi}\wedge\gamma^{s}_{\varphi}\;+\;\int\limits_{X}u_{\varepsilon}\,i\partial\bar{\partial}u\wedge i\partial\bar{\partial}\psi\wedge\Xi\;\right]
=\displaystyle= ∫Xi​∂u∧∂¯​u∧γψr+k∧γφs−limε→0+∫Xuε​i​∂∂¯​ψ∧(γφ−γψ)∧Ξ\displaystyle\int\limits_{X}i\partial u\wedge\bar{\partial}u\wedge\gamma^{r+k}_{\psi}\wedge\gamma^{s}_{\varphi}\;-\;\lim_{\varepsilon\rightarrow 0^{+}}\,\int\limits_{X}u_{\varepsilon}\,i\partial\bar{\partial}\psi\wedge(\gamma_{\varphi}-\gamma_{\psi})\wedge\Xi
≤\displaystyle\leq I+limε→0+∫Xi​∂uε∧∂¯​[ψ⁡(γφ−γψ)∧Ξ]\displaystyle I+\lim_{\varepsilon\rightarrow 0^{+}}\,\int\limits_{X}i\partial u_{\varepsilon}\wedge\bar{\partial}\left[\,\psi\,(\gamma_{\varphi}-\gamma_{\psi})\wedge\Xi\,\right]
=\displaystyle= limε→0+[∫Xi​∂uε∧∂¯​ψ∧γφ∧Ξ−∫Xi​∂uε∧∂¯​ψ∧γψ∧Ξ]\displaystyle\lim_{\varepsilon\rightarrow 0^{+}}\,\left[\;\int\limits_{X}i\partial u_{\varepsilon}\wedge\bar{\partial}\psi\wedge\gamma_{\varphi}\wedge\Xi\;-\;\int\limits_{X}i\partial u_{\varepsilon}\wedge\bar{\partial}\psi\wedge\gamma_{\psi}\wedge\Xi\;\right] (4.4)
=\displaystyle= ∫Xi​∂u∧∂¯​ψ∧γφ∧Ξ−∫Xi​∂u∧∂¯​ψ∧γψ∧Ξ.\displaystyle\int\limits_{X}i\partial u\wedge\bar{\partial}\psi\wedge\gamma_{\varphi}\wedge\Xi\;-\;\int\limits_{X}i\partial u\wedge\bar{\partial}\psi\wedge\gamma_{\psi}\wedge\Xi\,.

Set χ=φ\chi=\varphi or χ=ψ\chi=\psi. Then the Cauchy-Schwarz inequality implies

|∫Xi​∂u∧∂¯​ψ∧γχ∧Ξ|\displaystyle\left|\;\int\limits_{X}i\partial u\wedge\bar{\partial}\psi\wedge\gamma_{\chi}\wedge\Xi\;\right|
≤\displaystyle\leq (∫Xi​∂u∧∂¯​u∧γχ∧Ξ)1/2​(∫Xi​∂ψ∧∂¯​ψ∧γχ∧Ξ)1/2=0,\displaystyle\left(\;\int\limits_{X}i\partial u\wedge\bar{\partial}u\wedge\gamma_{\chi}\wedge\Xi\;\right)^{1/2}\left(\;\int\limits_{X}i\partial\psi\wedge\bar{\partial}\psi\wedge\gamma_{\chi}\wedge\Xi\;\right)^{1/2}=0\,,

by the inductive hypothesis. This combined with (4.4) implies (4.3) for kk. So at the end of the induction we get

0=∫Xi​∂u∧∂¯​u∧γn−1≥ηn−1​∫Xi​∂u∧∂¯​u∧θn−1≥0,0=\int\limits_{X}i\partial u\wedge\bar{\partial}u\wedge\gamma^{n-1}\geq\eta^{n-1}\int\limits_{X}i\partial u\wedge\bar{\partial}u\wedge\theta^{n-1}\geq 0\,,

which implies φ=ψ\varphi=\psi by elementary properties of plurisubharmonic functions.

Case λ>0\lambda>0. We start by proving the following lemma, which is a particular case of a more general result due to Yau. (See [Yau], sect. 6, page 376).

Lemma 6

. Let (X,ω)(X,\omega) be a compact Kähler manifold of complex dimension nn, let hh be a smooth function such that ∫Xωn=∫Xeh​ωn\int_{X}\omega^{n}=\int_{X}e^{h}\omega^{n} and φ∈𝒫ω\varphi\in{\cal P}_{\omega} a solution of the complex Monge-Ampère equation

(ω+i​∂∂¯​φ)n=eh+λ​φ​ωn,\displaystyle(\omega+i\partial\bar{\partial}\varphi)^{n}=e^{h+\lambda\varphi}\omega^{n}\,, (4.5)

λ>0\lambda>0. Consider also two solutions φ′​φ′′∈𝒫ω\varphi^{\prime}\,\varphi^{\prime\prime}\in{\cal P}_{\omega} of the complex Monge-Ampère equation (ω+i​∂∂¯​φ)n=eh​ωn(\omega+i\partial\bar{\partial}\varphi)^{n}=e^{h}\omega^{n} such that minX⁡φ′=0=maxX⁡φ′′\min_{X}\varphi^{\prime}=0=\max_{X}\varphi^{\prime\prime}. Then φ′′≤φ≤φ′\varphi^{\prime\prime}\leq\varphi\leq\varphi^{\prime}.

Proof. The argument is a simplification, in our particular case, of Yau’s original argument for the proof of thm. 4, sect. 6 in [Yau]. Set φ0′:=φ′,φ0′′:=φ′′\varphi^{\prime}_{0}:=\varphi^{\prime},\,\varphi^{\prime\prime}_{0}:=\varphi^{\prime\prime} and consider the solutions φj′,φj′′\varphi^{\prime}_{j},\,\varphi^{\prime\prime}_{j} of the complex Monge-Ampère equations given by the iteration

(ω+i​∂∂¯​φj′)n\displaystyle(\omega+i\partial\bar{\partial}\varphi^{\prime}_{j})^{n} =\displaystyle= eh+(λ+1)​φj′−φj−1′​ωn,\displaystyle e^{h+(\lambda+1)\varphi^{\prime}_{j}-\varphi^{\prime}_{j-1}}\,\omega^{n}\,, (4.6)
(ω+i​∂∂¯​φj′′)n\displaystyle(\omega+i\partial\bar{\partial}\varphi^{\prime\prime}_{j})^{n} =\displaystyle= eh+(λ+1)​φj′′−φj−1′′​ωn.\displaystyle e^{h+(\lambda+1)\varphi^{\prime\prime}_{j}-\varphi^{\prime\prime}_{j-1}}\,\omega^{n}\,. (4.7)

Notice that we can solve this equations even if the terms eh−φj−1′e^{h-\varphi^{\prime}_{j-1}}, eh−φj−1′′e^{h-\varphi^{\prime\prime}_{j-1}} are not normalized, see lem. 2 page 378 in [Yau]. Set k=λ+1k=\lambda+1 and consider

(ω+i​∂∂¯​φ1′)n=eh+k⁡(φ1′−φ0′)+λ​φ0′​ωn≥ek⁡(φ1′−φ0′)​eh​ωn=ek⁡(φ1′−φ0′)​(ω+i​∂∂¯​φ0′)n.(\omega+i\partial\bar{\partial}\varphi^{\prime}_{1})^{n}=e^{h+k(\varphi^{\prime}_{1}-\varphi^{\prime}_{0})+\lambda\varphi^{\prime}_{0}}\omega^{n}\geq e^{k(\varphi^{\prime}_{1}-\varphi^{\prime}_{0})}e^{h}\omega^{n}=e^{k(\varphi^{\prime}_{1}-\varphi^{\prime}_{0})}(\omega+i\partial\bar{\partial}\varphi^{\prime}_{0})^{n}\,.

At a maximum point of φ1′−φ0′\varphi^{\prime}_{1}-\varphi^{\prime}_{0} we have the inequality

(ω+i​∂∂¯​φ0′)n≥(ω+i​∂∂¯​φ1′)n.(\omega+i\partial\bar{\partial}\varphi^{\prime}_{0})^{n}\geq(\omega+i\partial\bar{\partial}\varphi^{\prime}_{1})^{n}\,.

By plugging this into the previous one, we deduce φ1′≤φ0′\varphi^{\prime}_{1}\leq\varphi^{\prime}_{0}. We now prove by induction the inequality φj′≤φj−1′\varphi^{\prime}_{j}\leq\varphi^{\prime}_{j-1}. In fact by dividing (4.6)j(\ref{MAith1})_{j} with (4.6)j−1(\ref{MAith1})_{j-1} we get

(ω+i​∂∂¯​φj′)n(ω+i​∂∂¯​φj−1′)n=ek⁡(φj′−φj−1′)−(φj−1′−φj−2′)≥ek⁡(φj′−φj−1′).\frac{(\omega+i\partial\bar{\partial}\varphi^{\prime}_{j})^{n}}{(\omega+i\partial\bar{\partial}\varphi^{\prime}_{j-1})^{n}}=e^{k(\varphi^{\prime}_{j}-\varphi^{\prime}_{j-1})-(\varphi^{\prime}_{j-1}-\varphi^{\prime}_{j-2})}\geq e^{k(\varphi^{\prime}_{j}-\varphi^{\prime}_{j-1})}\,.

At a maximum point of φj′−φj−1′\varphi^{\prime}_{j}-\varphi^{\prime}_{j-1} we again find the inequality

(ω+i​∂∂¯​φj′)n≤(ω+i​∂∂¯​φj−1′)n.(\omega+i\partial\bar{\partial}\varphi^{\prime}_{j})^{n}\leq(\omega+i\partial\bar{\partial}\varphi^{\prime}_{j-1})^{n}\,.

Combining this with the previous one we deduce φj′≤φj−1′\varphi^{\prime}_{j}\leq\varphi^{\prime}_{j-1}. We also prove by induction the inequality φj′′≤φj′\varphi^{\prime\prime}_{j}\leq\varphi^{\prime}_{j}, which is true by definition in the case j=0j=0. By dividing (4.6)j(\ref{MAith1})_{j} with (4.7)j(\ref{MAith2})_{j} we get

(ω+i​∂∂¯​φj′)n(ω+i​∂∂¯​φj′′)n=ek⁡(φj′−φj′′)−(φj−1′−φj−1′′)≤ek⁡(φj′−φj′′),\frac{(\omega+i\partial\bar{\partial}\varphi^{\prime}_{j})^{n}}{(\omega+i\partial\bar{\partial}\varphi^{\prime\prime}_{j})^{n}}=e^{k(\varphi^{\prime}_{j}-\varphi^{\prime\prime}_{j})-(\varphi^{\prime}_{j-1}-\varphi^{\prime\prime}_{j-1})}\leq e^{k(\varphi^{\prime}_{j}-\varphi^{\prime\prime}_{j})}\,,

by the induction hypothesis φj−1′′≤φj−1′\varphi^{\prime\prime}_{j-1}\leq\varphi^{\prime}_{j-1}. At a minimum point of φj′−φj′′\varphi^{\prime}_{j}-\varphi^{\prime\prime}_{j} we get

(ω+i​∂∂¯​φj′)n≥(ω+i​∂∂¯​φj′′)n,(\omega+i\partial\bar{\partial}\varphi^{\prime}_{j})^{n}\geq(\omega+i\partial\bar{\partial}\varphi^{\prime\prime}_{j})^{n}\,,

hence φj′′≤φj′\varphi^{\prime\prime}_{j}\leq\varphi^{\prime}_{j}. As a conclusion, we have proved the sequence of inequalities

φ0′′≤φj−1′′≤φj′′≤φj′≤φj−1′≤φ0′.\displaystyle\varphi^{\prime\prime}_{0}\leq\varphi^{\prime\prime}_{j-1}\leq\varphi^{\prime\prime}_{j}\leq\varphi^{\prime}_{j}\leq\varphi^{\prime}_{j-1}\leq\varphi^{\prime}_{0}\,. (4.8)

These inequalities imply 0<2​n+Δω​φj′≤C​Bj0<2n+\Delta_{\omega}\varphi^{\prime}_{j}\leq C\,B_{j}, where Bj>0B_{j}>0 satisfies the uniform estimate

0≥C1​Bj1n−1−(2​n+maxX⁡Δω​φj−1′)​Bj−1−C0,\displaystyle 0\geq C_{1}\,B_{j}^{\frac{1}{n-1}}-\left(2n+\max_{X}\Delta_{\omega}\varphi^{\prime}_{j-1}\right)B_{j}^{-1}-C_{0}\,, (4.9)

and C0,C1>0C_{0},\,C_{1}>0, which are obtained by applying the maximum principle in a way similar to Yau’s proof of the second order estimate for the solution of the Calabi conjecture [Yau]. (In the case n=1n=1 the uniform estimate 0<2​n+Δω​φj′≤C′0<2n+\Delta_{\omega}\varphi^{\prime}_{j}\leq C^{\prime} follows immediately from the inequalities (4.8).) Fix now a constant C3>0C_{3}>0 such that the inequality

C1​x1+1n−1≥(C0+2​C2)​x−C3,C_{1}\,x^{1+\frac{1}{n-1}}\geq(C_{0}+2C_{2})x-C_{3}\,,

hold for all x≥0x\geq 0. This implies by (4.9) the estimate

2​(2​n+Δω​φj′)≤2​C2​Bj≤(2​n+maxX⁡Δω​φj−1′)+C3,2(2n+\Delta_{\omega}\varphi^{\prime}_{j})\leq 2C_{2}\,B_{j}\leq\left(2n+\max_{X}\Delta_{\omega}\varphi^{\prime}_{j-1}\right)+C_{3}\,,

thus

2​n+maxX⁡Δω​φj′≤2−j​(2​n+maxX⁡Δω​φj−1′)+C3,2n+\max_{X}\Delta_{\omega}\varphi^{\prime}_{j}\leq 2^{-j}\left(2n+\max_{X}\Delta_{\omega}\varphi^{\prime}_{j-1}\right)+C_{3}\,,

by iteration. By taking the derivate in the Green Formula (see [Aub], Th. 4.13 page 108) we get the identity

dxφj′=−∫XdxGω(x,⋅)Δωφj′ωn,d_{x}\varphi^{\prime}_{j}=-\int\limits_{X}d_{x}G_{\omega}(x,\cdot)\,\Delta_{\omega}\varphi^{\prime}_{j}\,\omega^{n}\,,

which implies the estimate |∇ωφj′|ω≤Cω​maxX​Δω​φj′≤C|\nabla_{\omega}\varphi^{\prime}_{j}|_{\omega}\leq C_{\omega}\max_{X}\Delta_{\omega}\varphi^{\prime}_{j}\leq C. By applying the complex version of the Evans-Krylov theory [Ti2] we deduce the uniform estimate ‖φj′‖C2,α​(X)≤C′\|\varphi^{\prime}_{j}\|_{C^{2,\alpha}(X)}\leq C^{\prime}. This implies that the sequence (φj′)j(\varphi^{\prime}_{j})_{j} converges in the C2,αC^{2,\alpha}-topology to the unique solution φ\varphi of the complex Monge-Ampère equation (4.5). Then the conclusion follows from inequalities (4.8). □\Box

We consider now the unique family (ψj)j(\psi_{j})_{j}, ψj∈𝒫γj+εj​ω\psi_{j}\in{\cal P}_{\gamma_{j}+\varepsilon_{j}\omega} of smooth solutions of the complex Monge-Ampère equations

(γj+εj​ω+i​∂∂¯​ψj)n=fj​eλ​ψj​Ω,(\gamma_{j}+\varepsilon_{j}\omega+i\partial\bar{\partial}\psi_{j})^{n}=f_{j}\,e^{\lambda\,\psi_{j}}\Omega\,,

given by the Aubin-Yau’s solution of the Calabi conjecture. Consider also the solutions ψj′\psi^{\prime}_{j}, ψj′′\psi^{\prime\prime}_{j}, minX⁡ψj′=0=maxX⁡ψj′′\min_{X}\psi^{\prime}_{j}=0=\max_{X}\psi^{\prime\prime}_{j} of the complex Monge-Ampère equation

(γj+εj​ω+i​∂∂¯​φ)n=fj​Ω.(\gamma_{j}+\varepsilon_{j}\omega+i\partial\bar{\partial}\varphi)^{n}=f_{j}\,\Omega\,.

By applying lemma 6 we deduce ψj′′≤ψj≤ψj′\psi^{\prime\prime}_{j}\leq\psi_{j}\leq\psi^{\prime}_{j} for all jj. By the same argument in the case λ=0\lambda=0, we deduce ‖ψj′‖C0​(X),‖ψj′′‖C0​(X)≤C\|\psi^{\prime}_{j}\|_{C^{0}(X)},\,\|\psi^{\prime\prime}_{j}\|_{C^{0}(X)}\leq C, thus ‖ψj‖C0​(X)≤C\|\psi_{j}\|_{C^{0}(X)}\leq C and so

‖fj​eλ​ψj‖L​logn+δ​L​(X)≤C′​eλ​C​‖f‖L​logn+δ​L​(X).\|f_{j}\,e^{\lambda\psi_{j}}\|_{L\log^{n+\delta}L(X)}\leq C^{\prime}e^{\lambda C}\|f\|_{L\log^{n+\delta}L(X)}\,.

This fact allows us to apply theorem 3, B as in the case λ=0\lambda=0 in order to get a sequence of solutions (ψj)j(\psi_{j})_{j} convergent in the uniform topology to some ψ∈𝒫γ∩C0​(X)\psi\in{\cal P}_{\gamma}\cap C^{0}(X). This implies the convergence of the weak limits

(γ+i​∂∂¯​ψ)n=limj→+∞(γj+εj​ω+i​∂∂¯​ψj)n=limj→+∞fj​eλ​ψj​Ω=f​eλ​ψ​Ω.(\gamma+i\partial\bar{\partial}\psi)^{n}=\lim_{j\rightarrow+\infty}(\gamma_{j}+\varepsilon_{j}\omega+i\partial\bar{\partial}\psi_{j})^{n}=\lim_{j\rightarrow+\infty}f_{j}e^{\lambda\psi_{j}}\,\Omega=fe^{\lambda\psi}\,\Omega\,.

The integral estimate in the statement of theorem 6 follows immediately from theorem 3, A and from the inequalities ψj′′≤ψj≤ψj′\psi^{\prime\prime}_{j}\leq\psi_{j}\leq\psi^{\prime}_{j}. We prove now the uniqueness of the solutions. Let φ∈𝒫^γ\varphi\in\hat{\cal P}_{\gamma} be another solution. The fact that φ≤C\varphi\leq C implies

‖f​eλ​φ‖L​logn+δ​L​(X)≤eλ​C​‖f‖L​logn+δ​L​(X),\|f\,e^{\lambda\varphi}\|_{L\log^{n+\delta}L(X)}\leq e^{\lambda C}\|f\|_{L\log^{n+\delta}L(X)}\,,

which allows us to solve the degenerate complex Monge-Ampère equation

(γ+i​∂∂¯​u)n=f​eλ​φ​Ω,(\gamma+i\partial\bar{\partial}u)^{n}=f\,e^{\lambda\varphi}\Omega\,,

with u∈𝒫γ0∩C0​(X)u\in{\cal P}^{0}_{\gamma}\cap C^{0}(X). By the uniqueness result in the case λ=0\lambda=0 we deduce u=φ−supXφu=\varphi-\sup_{X}\varphi, thus φ∈𝒫γ∩C0​(X)\varphi\in{\cal P}_{\gamma}\cap C^{0}(X). By applying the comparison principle we get

∫φ<ψγψn≤∫φ<ψγφn=∫φ<ψeλ⁡(φ−ψ)​γψn,\int\limits_{\varphi<\psi}\gamma^{n}_{\psi}\,\leq\,\int\limits_{\varphi<\psi}\gamma^{n}_{\varphi}\,=\,\int\limits_{\varphi<\psi}e^{\lambda(\varphi-\psi)}\gamma^{n}_{\psi}\,,

which implies ∫φ<ψγψn=0\int_{\varphi<\psi}\gamma^{n}_{\psi}=0 since eλ⁡(φ−ψ)<1e^{\lambda(\varphi-\psi)}<1. This implies φ≥ψ\varphi\geq\psi γψn\gamma^{n}_{\psi}-almost everywhere, thus γφn=eλ⁡(φ−ψ)​γψn≤γψn\gamma^{n}_{\varphi}=e^{\lambda(\varphi-\psi)}\gamma^{n}_{\psi}\leq\gamma^{n}_{\psi} γψn\gamma^{n}_{\psi}-almost everywhere. By symmetry we also deduce γψn≤γφn\gamma^{n}_{\psi}\leq\gamma^{n}_{\varphi} γφn\gamma^{n}_{\varphi}-almost everywhere. The fact that φ,ψ\varphi,\,\psi are solutions of our complex Monge-Ampère equation implies that a property holds γψn\gamma^{n}_{\psi}-almost everywhere if and only if it holds Ω\Omega-almost everywhere and the same for γφn\gamma^{n}_{\varphi}. We thus infer γψn=γφn\gamma^{n}_{\psi}=\gamma^{n}_{\varphi}, which implies ψ=φ\psi=\varphi by the expression of the Monge-Ampère equation. □\Box

The following lemma gives us an important class of functions for the right hand side of the degenerate complex Monge-Ampère equation.

Lemma 7

. Let XX be a compact complex manifold, let Ω>0\Omega>0 be a smooth volume form and let σj∈H0​(X,Ej)\sigma_{j}\in H^{0}(X,E_{j}), τr∈H0​(X,Fr)\tau_{r}\in H^{0}(X,F_{r}), j=1,…,Nj=1,...,N, r=1,…,Mr=1,...,M be, non identically zero, holomorphic sections of some holomorphic vector bundles over XX such that the integral condition

∫X∏j=1N|σj|2​lj⋅∏r=1M|τr|−2​hr​Ω<+∞\displaystyle\int\limits_{X}\,\prod\limits_{j=1}^{N}|\sigma_{j}|^{2l_{j}}\cdot\prod\limits_{r=1}^{M}|\tau_{r}|^{-2h_{r}}\,\Omega<+\infty

holds for some real numbers lj≥0,hr≥0l_{j}\geq 0,\,h_{r}\geq 0. Then the integrand function belongs to some LpL^{p} space, p>1p>1 and the family of functions

Gε:=∏j=1N(|σj|2+εA)lj⋅∏r=1M(|τr|2+ε)−hr,\displaystyle G_{\varepsilon}:=\prod\limits_{j=1}^{N}(|\sigma_{j}|^{2}+\varepsilon^{A})^{l_{j}}\cdot\prod\limits_{r=1}^{M}(|\tau_{r}|^{2}+\varepsilon)^{-h_{r}}\,,

ε∈[0,1)\varepsilon\in[0,1), A:=(∑rhr+1)/(minj⁡lj)A:=(\sum_{r}h_{r}+1)/(\min_{j}l_{j}), converges in LpL^{p}-norm to function G0G_{0} when ε→0\varepsilon\rightarrow 0.

Proof. We define the coherent complex analytic sheaves 𝒥σj:=∑p𝒪X​σj,p{\cal J}_{\sigma_{j}}:=\sum_{p}{\cal O}_{X}\sigma_{j,p} and 𝒥τr:=∑q𝒪X​τr,q⊂𝒪X{\cal J}_{\tau_{r}}:=\sum_{q}{\cal O}_{X}\tau_{r,q}\subset{\cal O}_{X}, with σj=(σj,p)p\sigma_{j}=(\sigma_{j,p})_{p} , τr=(τr,q)q\tau_{r}=(\tau_{r,q})_{q} for some local holomorphic trivializations of the vector bundles EjE_{j}, FrF_{r}. Clearly the definition is independent of the local trivialization, thus this sheaves are globally well defined. By the Hironaka desingularization theorem [Hir] we can find a proper bimeromorphic morphism μ:X~→X\mu:\tilde{X}\rightarrow X of compact complex manifolds such that there exists a family (Hs)s(H_{s})_{s}, Hs⊂X~H_{s}\subset\tilde{X} of smooth hypersurfaces with normal crossing in X~\tilde{X} such that μ⁡(⋃sHs)=⋃jV⁡(σj)∪⋃rV⁡(τr)\mu\left(\bigcup_{s}H_{s}\right)=\bigcup_{j}V(\sigma_{j})\cup\bigcup_{r}V(\tau_{r}),

KX~=μ∗​KX+∑sas​Hs,as∈ℕ,K_{\tilde{X}}=\mu^{*}K_{X}+\sum_{s}\,a_{s}\,H_{s}\,,\quad a_{s}\in\mathbb{N}\,,

and μ∗𝒥σj=𝒪X~(−∑sbj,sHs)\mu^{*}{\cal J}_{\sigma_{j}}={\cal O}_{\tilde{X}}\left(-\sum_{s}\,b_{j,s}\,H_{s}\right), μ∗𝒥τr=𝒪X~(−∑scr,sHs)\mu^{*}{\cal J}_{\tau_{r}}={\cal O}_{\tilde{X}}\left(-\sum_{s}\,c_{r,s}\,H_{s}\right), bj,sb_{j,s}, cr,s∈ℕc_{r,s}\in\mathbb{N} for all j,rj,r. The fact that μ\mu is a holomorphic map implies dμ⊗ℝ𝕀ℂ=∂μ⊕∂μ¯d\mu\otimes_{{}_{\mathbb{R}}}\mathbb{I}_{{}_{\mathbb{C}}}=\partial\mu\oplus\overline{\partial\mu}, with ∂μ∈H0​(X~,Λ1,0​TX~∗⊗μ∗​TX1,0)\partial\mu\in H^{0}(\tilde{X},\Lambda^{1,0}T^{*}_{\tilde{X}}\otimes\mu^{*}T^{1,0}_{X}). Thus the divisor of the Jacobian Λn​∂μ∈H0​(X~,KX~−μ∗​KX)\Lambda^{n}\partial\mu\in H^{0}(\tilde{X},K_{\tilde{X}}-\mu^{*}K_{X}) of μ\mu is by definition ∑sas​Hs\sum_{s}\,a_{s}\,H_{s}. On the other hand the invariance of the integral by orientation preserving diffeomorphisms implies

Ip\displaystyle I_{p} :⁣=\displaystyle:= ∫X∏j=1N|σj|2​lj​p⋅∏r=1M|τr|−2​hr​p​Ω\displaystyle\int\limits_{X}\,\prod\limits_{j=1}^{N}|\sigma_{j}|^{2l_{j}p}\cdot\prod\limits_{r=1}^{M}|\tau_{r}|^{-2h_{r}p}\,\Omega
=\displaystyle= ∫X~∏j=1N|σj∘μ|2​lj​p⋅∏r=1M|τr∘μ|−2​hr​p​(Ω∘μ)⋅(Λn​∂μ)∧(Λn​∂μ)¯.\displaystyle\int\limits_{\tilde{X}}\,\prod\limits_{j=1}^{N}|\sigma_{j}\circ\mu|^{2l_{j}p}\cdot\prod\limits_{r=1}^{M}|\tau_{r}\circ\mu|^{-2h_{r}p}\,(\Omega\circ\mu)\cdot(\Lambda^{n}\partial\mu)\wedge\overline{(\Lambda^{n}\partial\mu)}\,.

For any open set U⊂X~U\subset\tilde{X} we denote by {s1,…,sm}:={s|Hs∩U≠∅}\{s_{1},...,s_{m}\}:=\{s\,|\,H_{s}\cap U\not=\emptyset\}. For any point in X~\tilde{X} one can find a coordinate neighborhood U:={|zk|<1}U:=\{|z_{k}|<1\} such that Hst={zt=0}H_{s_{t}}=\{z_{t}=0\}, t=1,…,m≤nt=1,...,m\leq n. With respect to this coordinates, we have

(Ω∘μ)⋅(Λn​∂μ)∧(Λn​∂μ)¯=ρ​∏t=1m|zt|2​ast​in2​d​z1∧…∧d​zn∧d​z¯1∧…∧d​z¯n,(\Omega\circ\mu)\cdot(\Lambda^{n}\partial\mu)\wedge\overline{(\Lambda^{n}\partial\mu)}=\rho\prod\limits_{t=1}^{m}|z_{t}|^{2a_{s_{t}}}\,i^{n^{2}}dz_{1}\wedge...\wedge dz_{n}\wedge d\bar{z}_{1}\wedge...\wedge d\bar{z}_{n}\,,

ρ>0\rho>0, ρ∈C∞​(U)\rho\in C^{\infty}(U) and σj,p∘μ=fj,p​∏t=1mztbj,st\sigma_{j,p}\circ\mu=f_{j,p}\prod_{t=1}^{m}z_{t}^{b_{j,s_{t}}}, τr,q∘μ=gr,q​∏t=1mztcr,st\tau_{r,q}\circ\mu=g_{r,q}\prod_{t=1}^{m}z_{t}^{c_{r,s_{t}}}, fj,p,gr,q∈𝒪⁡(U)f_{j,p},\,g_{r,q}\in{\cal O}(U). Then modulo factors that are bounded away from 00 and ∞\infty, we find

|σj∘μ|2\displaystyle|\sigma_{j}\circ\mu|^{2} ∼\displaystyle\thicksim (∑p|fj,p|2)​∏t=1m|zt|2​bj,st,\displaystyle\left(\sum_{p}|f_{j,p}|^{2}\right)\prod_{t=1}^{m}|z_{t}|^{2b_{j,s_{t}}}\,,
|τr∘μ|2\displaystyle|\tau_{r}\circ\mu|^{2} ∼\displaystyle\thicksim (∑q|gr,q|2)​∏t=1m|zt|2​cr,st,\displaystyle\left(\sum_{q}|g_{r,q}|^{2}\right)\prod_{t=1}^{m}|z_{t}|^{2c_{r,s_{t}}}\,,

with ∑p|fj,p|2>0\sum_{p}|f_{j,p}|^{2}>0, ∑q|gr,q|2>0\sum_{q}|g_{r,q}|^{2}>0. The latter nonvanishing property follows from the fact that the terms |∑sbj,s​Hs|=μ−1​V​(σj)|\sum_{s}\,b_{j,s}\,H_{s}|=\mu^{-1}V(\sigma_{j}), |∑scr,s​Hs|=μ−1​V​(τr)|\sum_{s}\,c_{r,s}\,H_{s}|=\mu^{-1}V(\tau_{r}), (σj,p∘μ)p(\sigma_{j,p}\circ\mu)_{p} correspond to local generators of the sheaf 𝒪X~​(∑sbj,s​Hs){\cal O}_{\tilde{X}}\left(\sum_{s}\,b_{j,s}\,H_{s}\right) and (τr,q∘μ)q(\tau_{r,q}\circ\mu)_{q} are local generators of the sheaf 𝒪X~​(∑scr,s​Hs){\cal O}_{\tilde{X}}\left(\sum_{s}\,c_{r,s}\,H_{s}\right). We infer

∏j=1N|σj|2​lj⋅∏r=1M|τr|−2​hr∼∏t=1m|zt|−2​dst,\prod\limits_{j=1}^{N}|\sigma_{j}|^{2l_{j}}\cdot\prod\limits_{r=1}^{M}|\tau_{r}|^{-2h_{r}}\thicksim\prod_{t=1}^{m}|z_{t}|^{-2d_{s_{t}}}\,,

with ds:=Cs​H−Bs​Ld_{s}:=C_{s}H-B_{s}L, L:=∑jljL:=\sum_{j}l_{j}, H:=∑rhrH:=\sum_{r}h_{r}, Bs:=∑jbj,sB_{s}:=\sum_{j}b_{j,s} and Cs:=∑rcr,sC_{s}:=\sum_{r}c_{r,s}. Set also T:={t∈{1,…,m}| 0<dst−ast}T:=\{t\in\{1,...,m\}\,|\,0<d_{s_{t}}-a_{s_{t}}\}. The hypothesis I0<+∞I_{0}<+\infty implies dst<1+astd_{s_{t}}<1+a_{s_{t}} for all t∈Tt\in T. Thus there exists pU>1p_{U}>1 such that pU​dst<1+astp_{U}d_{s_{t}}<1+a_{s_{t}} for all t∈Tt\in T. If (Uα)α(U_{\alpha})_{\alpha} is a finite covering of X~\tilde{X}, with UαU_{\alpha} as UU and p:=minα⁡pUα>1p:=\min_{\alpha}p_{U_{\alpha}}>1 then Ip<+∞I_{p}<+\infty. This proves the first claim in the statement of lemma 7. In order to prove the convergence in the LpL^{p} norm of the functions GεG_{\varepsilon} we distinguish two cases. In the case where lj=0l_{j}=0 for all jj, the claim follows imediately from the monotone convergence theorem. The other possible case is lj>0l_{j}>0 for all jj. In this case we set l:=minj⁡lj>0l:=\min_{j}l_{j}>0. Then our setting implies A=(H+1)/lA=(H+1)/l. For all ε,ρ∈(0,1)\varepsilon,\rho\in(0,1) consider the sequence of inequalities

∫X∏j=1N|σj|2​lj​p⋅∏r=1M(|τr|2+ε)−hr​p​Ω≤∫XGεp​Ω\displaystyle\int\limits_{X}\,\prod\limits_{j=1}^{N}|\sigma_{j}|^{2l_{j}p}\cdot\prod\limits_{r=1}^{M}(|\tau_{r}|^{2}+\varepsilon)^{-h_{r}p}\,\Omega\;\leq\;\int\limits_{X}G_{\varepsilon}^{p}\,\Omega
=\displaystyle= ∫⋃t=1N{ρ|σt|2<εA}GεpΩ+∫⋂t=1N{ρ|σt|2≥εA}GεpΩ\displaystyle\int\limits_{\bigcup_{t=1}^{N}\{\rho|\sigma_{t}|^{2}\,<\,\varepsilon^{A}\}}G_{\varepsilon}^{p}\,\Omega\;+\;\int\limits_{\bigcap_{t=1}^{N}\{\rho|\sigma_{t}|^{2}\,\geq\,\varepsilon^{A}\}}G_{\varepsilon}^{p}\,\Omega
≤\displaystyle\leq ∑t=1N∫{ρ|σt|2<εA}GεpΩ+∫⋂t=1N{ρ|σt|2≥εA}GεpΩ\displaystyle\sum_{t=1}^{N}\;\int\limits_{\{\rho|\sigma_{t}|^{2}\,<\,\varepsilon^{A}\}}G_{\varepsilon}^{p}\,\Omega\;+\;\int\limits_{\bigcap_{t=1}^{N}\{\rho|\sigma_{t}|^{2}\,\geq\,\varepsilon^{A}\}}G_{\varepsilon}^{p}\,\Omega
≤\displaystyle\leq ∑t=1N∫{ρ|σt|2<εA}ε−H​p∏j=1N(|σj|2+εA)lj​pΩ\displaystyle\sum_{t=1}^{N}\;\int\limits_{\{\rho|\sigma_{t}|^{2}\,<\,\varepsilon^{A}\}}\varepsilon^{-Hp}\,\prod\limits_{j=1}^{N}(|\sigma_{j}|^{2}+\varepsilon^{A})^{l_{j}p}\,\Omega
+\displaystyle+ ∫⋂t=1N{ρ|σt|2≥εA}∏j=1N(1+ρ)lj​p|σj|2​lj​p⋅∏r=1M(|τr|2+ε)−hr​pΩ\displaystyle\int\limits_{\bigcap_{t=1}^{N}\{\rho|\sigma_{t}|^{2}\,\geq\,\varepsilon^{A}\}}\,\prod\limits_{j=1}^{N}(1+\rho)^{l_{j}p}|\sigma_{j}|^{2l_{j}p}\cdot\prod\limits_{r=1}^{M}(|\tau_{r}|^{2}+\varepsilon)^{-h_{r}p}\,\Omega
≤\displaystyle\leq ∑t=1N(1+ρ−1)L​pε(A​l−H)​p∫{ρ|σt|2<εA}∏j≠t(|σj|2+εA)lj​pΩ\displaystyle\sum_{t=1}^{N}(1+\rho^{-1})^{Lp}\,\varepsilon^{(Al-H)p}\int\limits_{\{\rho|\sigma_{t}|^{2}\,<\,\varepsilon^{A}\}}\,\prod\limits_{j\not=t}(|\sigma_{j}|^{2}+\varepsilon^{A})^{l_{j}p}\,\Omega
+\displaystyle+ (1+ρ)L​p​∫X∏j=1N|σj|2​lj​p⋅∏r=1M|τr|−2​hr​p​Ω\displaystyle(1+\rho)^{Lp}\int\limits_{X}\,\prod\limits_{j=1}^{N}|\sigma_{j}|^{2l_{j}p}\cdot\prod\limits_{r=1}^{M}|\tau_{r}|^{-2h_{r}p}\,\Omega
≤\displaystyle\leq (1+ρ−1)L​p​εp​C+(1+ρ)L​p​∫XG0p​Ω,\displaystyle(1+\rho^{-1})^{Lp}\,\varepsilon^{p}C+(1+\rho)^{Lp}\int\limits_{X}G^{p}_{0}\,\Omega\,,

where C>0C>0 is a constant uniform in ε\varepsilon. Thus by letting ε→0+\varepsilon\rightarrow 0^{+} and by applying the increasing monotone convergence theorem to the first integral in the previous inequalities, we obtain

∫XG0p​Ω≤lim infε→0+∫XGεp​Ω≤lim supε→0+∫XGεp​Ω≤(1+ρ)L​p​∫XG0p​Ω.\int\limits_{X}G_{0}^{p}\,\Omega\leq\liminf_{\varepsilon\rightarrow 0^{+}}\int\limits_{X}G_{\varepsilon}^{p}\,\Omega\leq\limsup_{\varepsilon\rightarrow 0^{+}}\int\limits_{X}G_{\varepsilon}^{p}\,\Omega\leq(1+\rho)^{Lp}\int\limits_{X}G_{0}^{p}\,\Omega\,.

Then the conclusion follows by letting ρ→0+\rho\rightarrow 0^{+} and by the fact that GεG_{\varepsilon} converges pointwise almost everywhere to G0G_{0} as ε→0+\varepsilon\rightarrow 0^{+}. □\Box

Original mathematics by the credited authors. Source-backed reader collection; mathematical self-containment is not assessed.