Solution (source code)

= Solution

One prescribes analytic <Cauchy data>: the value of $u$ and one first derivative transverse to $\Sigma$, for example
$$
u|_\Sigma=\phi,
\qquad
\partial_\nu u|_\Sigma=\psi,
$$
where $\phi$ and $\psi$ are real analytic on $\Sigma$. Being a <non-characteristic hypersurface> allows the equation to solve for the second derivative in the transverse direction. The <Cauchy-Kovalevskaya theorem> then gives \b[one and only one local real analytic solution near $p$].