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Lemma 8.6.2B8367971A40D

Lemma 8.6.2.B8367971A40D Every continuous admissible $\varphi $ on $X$ is the uniform limit of smooth strictly admissible functions.

Proof. Fix a smooth $h\geq \varphi $ and a constant

\[ b>\max \left\{ 1,\left\| H_ m(h)/\omega ^ n\right\| _\infty \right\} . \]

For each positive integer $N$ solve, by the preceding lemma,

\[ H_ m(w_ N)=b e^{N(w_ N-h)}\omega ^ n. \]

At a positive maximum of $w_ N-h$, the form $\omega +\mathrm{dd}^{\mathrm{c}}h$ lies above the strictly admissible form $\omega +\mathrm{dd}^{\mathrm{c}}w_ N$, hence is admissible there. Monotonicity would give $b e^{N(w_ N-h)}\leq H_ m(h)/\omega ^ n<b$, a contradiction. Thus $w_ N\leq h$. The preceding zero-order estimate also gives

\[ \| w_ N\| _\infty \leq M_ N:=\| h\| _\infty +\frac{\log b}{N}. \]

Let $x_ N$ maximize $\varphi -(1+N^{-1})w_ N$. The smooth positive form $T_ N=(\omega +\mathrm{dd}^{\mathrm{c}}w_ N)^{m-1}\wedge \omega ^{n-m}$ defines a strictly elliptic linear operator. Admissibility gives $(\omega +\mathrm{dd}^{\mathrm{c}}\varphi )\wedge T_ N\geq 0$ in distributions. Its linear maximum principle, applied to the upper test $(1+N^{-1})w_ N$ plus the maximum value, gives at $x_ N$

\[ 0\leq \bigl (\omega +(1+N^{-1})\mathrm{dd}^{\mathrm{c}}w_ N\bigr )\wedge T_ N. \]

This application is to a continuous distributional subsolution of a smooth strictly elliptic operator. It does not assume a second derivative of $\varphi $. Writing $d_ N=H_ m(w_ N)/\omega ^ n$, polarized Gårding positivity yields

\[ (N+1)d_ N\geq \omega \wedge T_ N/\omega ^ n \geq d_ N^{(m-1)/m}. \]

Therefore, at this maximum point,

\[ w_ N-h\geq -E_ N,\qquad E_ N=\frac{m\log (N+1)+\log b}{N}. \]

Since $\varphi \leq h$, the maximum of $\varphi -(1+N^{-1})w_ N$ is at most $E_ N+M_ N/N$. It follows on all of $X$ that

\[ \varphi -E_ N-2M_ N/N\leq w_ N\leq h. \]

Given $\delta >0$, choose an ordinary smooth majorant $\varphi \leq h\leq \varphi +\delta $, and then $N$ so large that $E_ N+2M_ N/N\leq \delta $. The resulting $w_ N$ is strictly admissible and within $\delta $ of $\varphi $. Let $\delta \downarrow 0$. No monotonicity of the chosen approximants is needed. $\square$

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