Show that = / = (1/) arctan (y/x) is harmonic in the upper half-plane and satisfies

Show that Φ = θ/π = (1/π) arctan (y/x) is harmonic in the upper half-plane and satisfies the boundary condition Φ (x, 0) = 1 if x < 0 and 0 if x > 0, and the corresponding complex potential is F(z) = -(i/π) Ln Z.