[step:Use the coercive estimate to solve $\bar\partial U_m=F_m$ with the sharp $m^{-1}$ bound]For each integer $r\ge 0$, let $H_{m,r}$ be the [Hilbert space](/page/Hilbert%20Space) completion of smooth $E_m$-valued $(n,r)$-forms in the norm $\|\cdot\|_{L^2(X,\omega,g_m)}$. Define the closed densely defined operator
\begin{align*}
D_{m,r}:\operatorname{Dom}(D_{m,r})\subset H_{m,r}&\to H_{m,r+1} \\
\alpha&\mapsto \bar\partial\alpha
\end{align*}
as the maximal closed extension of $\bar\partial$ from smooth forms, and let $D_{m,r}^*$ denote its Hilbert-space adjoint. The estimate from the previous step extends by density to every
\begin{align*}
\alpha\in \operatorname{Dom}(D_{m,q})\cap \operatorname{Dom}(D_{m,q-1}^*)
\end{align*}
and gives
\begin{align*}
\|D_{m,q}\alpha\|_{L^2(X,\omega,g_m)}^2
+
\|D_{m,q-1}^*\alpha\|_{L^2(X,\omega,g_m)}^2
\ge
\frac{\lambda}{2}m\|\alpha\|_{L^2(X,\omega,g_m)}^2.
\end{align*}
Set
\begin{align*}
c_m:=\frac{\lambda}{2}m.
\end{align*}
We now use the standard closed-range estimate for Hilbert complexes (citing a result not yet in the wiki: closed-range minimal-solution theorem for Hilbert complexes). In the following form, it says that for a closed Hilbert complex
\begin{align*}
H_{m,q-1}\xrightarrow{D_{m,q-1}}H_{m,q}\xrightarrow{D_{m,q}}H_{m,q+1},
\end{align*}
if the estimate
\begin{align*}
c_m\|\alpha\|_{L^2(X,\omega,g_m)}^2
\le
\|D_{m,q}\alpha\|_{L^2(X,\omega,g_m)}^2
+
\|D_{m,q-1}^*\alpha\|_{L^2(X,\omega,g_m)}^2
\end{align*}
holds for all $\alpha\in \operatorname{Dom}(D_{m,q})\cap\operatorname{Dom}(D_{m,q-1}^*)$, then $\operatorname{Ran}D_{m,q-1}$ is closed, $\ker D_{m,q}=\operatorname{Ran}D_{m,q-1}$, and every $F\in\ker D_{m,q}$ has a unique minimal solution
\begin{align*}
U\in \operatorname{Dom}(D_{m,q-1})\cap(\ker D_{m,q-1})^\perp
\end{align*}
such that
\begin{align*}
D_{m,q-1}U=F
\end{align*}
and
\begin{align*}
\|U\|_{L^2(X,\omega,g_m)}^2\le c_m^{-1}\|F\|_{L^2(X,\omega,g_m)}^2.
\end{align*}
In the Dolbeault complex, the same theorem gives the weak normal condition
\begin{align*}
D_{m,q-2}^*U=0
\end{align*}
for the minimal solution, with this term omitted when $q=1$. This quoted Hilbert-complex theorem packages the domain statements, closed-range conclusion, normal equation, and minimal-norm estimate; no additional differentiation of a weak Laplacian equation is being used here.
Since $F_m$ is smooth and $\bar\partial F_m=0$, we have $F_m\in\ker D_{m,q}$. Applying the closed-range theorem gives an $E_m$-valued $(n,q-1)$-form
\begin{align*}
U_m\in\operatorname{Dom}(D_{m,q-1})
\end{align*}
such that
\begin{align*}
\bar\partial U_m=D_{m,q-1}U_m=F_m
\end{align*}
and
\begin{align*}
\|U_m\|_{L^2(X,\omega,g_m)}^2
\le
\frac{2}{\lambda m}\|F_m\|_{L^2(X,\omega,g_m)}^2.
\end{align*}[/step]