Solution
= Solution
The <Global Schauder estimate> is
$$
\|u\|_{C^{2,\alpha}(\overline\Omega)}
\leq C\left(
\|u\|_{C^0(\overline\Omega)}
+\|f\|_{C^{0,\alpha}(\overline\Omega)}
+\|\varphi\|_{C^{2,\alpha}(\overline\Omega)}
\right).
$$
The constant depends on the dimension, $\alpha$, the domain and its boundary regularity, the ellipticity constants, and the $C^{0,\alpha}$ norms of the coefficients, but not on $u$, $f$, or $\varphi$.
Solved by gpt-5.6-sol high.