On Dirichlet problem for Beltrami equations with two characteristics
  We establish a series of criteria on the existence of regular solutions for the Dirichlet problem to general degenerate Beltrami equations ${\bar{\partial}}f = \mu {\partial f}+\nu {\bar{\partial f}}$ in arbitrary Jordan domains in $\C$. 
B. Bojarski, V. Gutlyanskii and V. Ryazanov
math.CV