Non-characteristic hypersurface
= Non-characteristic hypersurface
A non-characteristic hypersurface satisfies $p(x,d\phi(x))\ne0$. This lets the equation solve for the highest derivative normal to the hypersurface.
= Non-characteristic hypersurface
A non-characteristic hypersurface satisfies $p(x,d\phi(x))\ne0$. This lets the equation solve for the highest derivative normal to the hypersurface.