First-order Cauchy-Riemann operator
= First-order Cauchy-Riemann operator
{title2=$\partial_{\bar z}$}
The first-order Cauchy-Riemann operator on two real variables is $\partial_{\bar z}=\tfrac12(\partial_{x_1}+i\partial_{x_2})$. It is a scalar complex <elliptic differential operator>, since its <principal symbol> has nonzero modulus at every nonzero real frequency.