Solution (source code)

= Solution

Differentiate the <Cauchy-Riemann equations> and use equality of mixed <partial derivatives>, which holds because <holomorphic functions> are smooth:
$$
\boxed{\Delta u=(v_y)_x-(v_x)_y=0,\qquad\Delta v=-(u_y)_x+(u_x)_y=0.}
$$
Thus both parts are <harmonic functions>.