Solution
= Solution
Since $\mathbf V=\nabla u$, its <divergence> is the <Laplacian> of the velocity potential. Using the <Cauchy-Riemann equations> and equality of mixed <partial derivatives> gives
$$
\boxed{\nabla\cdot\mathbf V=u_{xx}+u_{yy}=(v_y)_x-(v_x)_y=0.}
$$
Thus this is an <incompressible flow>, and $u$ is a <harmonic function>.