I'm having a really hard time trying to figure out when to use the Cauchy-Riemann equations, u_x = v_y and u_y = -v_x. My textbook says that they are necessary, but not sufficient conditions for differentiability. My textbook also says that they can be used to show that a function is not differentiable at a point, by showing that the CR equations do not hold. So is that all they can be used for, to show non-differentiability?