Prompt: Elliptic Pucci conjecture

We used this Markdown research procedure together with the following prompt.

• mathematical_research_goal.md
• Plain text prompt

I am attaching `mathematical_research_goal.md`.
Read it completely and use it as the research procedure for this task.

Resolve the exact problem below. Seek a complete, rigorous solution, not merely
an approach or a literature-status answer. Preserve every hypothesis and quantifier.

EXECUTION_MODE: AUTO
PROJECT_WINDOW_BUDGET: 6 hours

Use that window only through genuine long-running execution with observable
timing. Otherwise do substantive work in the available execution block and save
a resumable checkpoint at its actual boundary. Do not invent elapsed time or
background continuation.

<TARGET_PROBLEM_BEGIN>

```latex
Fix an integer $n\ge2$, $0<\delta<1/n$, and $1\le p<\infty$.
Let $B_1=\{x\in\mathbb R^n:|x|<1\}$, where $|\cdot|$ is
the Euclidean norm.

Consider all Lebesgue-measurable symmetric matrix fields
$A=(a_{ij}):B_1\to\mathbb R^{n\times n}$ satisfying,
for almost every $x$,
\[
  \operatorname{tr}A(x)=1,
  \qquad
  \xi^T A(x)\xi\ge\delta|\xi|^2
  \quad\text{for every }\xi\in\mathbb R^n,
\]
and define
\[
  L_Au=\sum_{i,j=1}^n a_{ij}\,
  \frac{\partial^2u}{\partial x_i\partial x_j}.
\]

The conjecture asserts that a finite constant $C=C(n,\delta,p)>0$
making
\[
  \max_{x\in\overline{B_1}}|u(x)|
  \le C\left(\int_{B_1}|L_Au(x)|^p\,dx\right)^{1/p}
\]
hold for every such $A$ and every real-valued $u$ continuous on
$\overline{B_1}$, twice continuously differentiable in $B_1$,
zero on $\partial B_1$, and with the displayed integral finite,
exists if and only if
\[
  \boxed{\displaystyle
  p>\max\left\{\frac n2,\;n\bigl[1-(n-1)\delta\bigr]\right\}.}
\]
Here $dx$ is Lebesgue measure. The constant is independent of
$A$ and $u$; the strict inequality excludes the endpoint.
```

<TARGET_PROBLEM_END>

First preserve the exact target in `checkpoint.md` when file writing is available.
Keep normalization brief, perform a concrete mathematical probe, and then develop
the strongest route. Continue beyond setup while resources remain. Distinguish
conditional progress from a solution, and audit a complete candidate before
claiming a resolution.

Any notes or prior attempts I supply outside the target are context, not extra
hypotheses unless I explicitly designate them as such.