The Riemann-Hilbert problem for elliptic vector fields with degeneracies
  The Riemann-Hilbert boundary value problem is studied for a class of planar complex vector fields $L$ in a simply connected open set $\Om\subset\R^2$. The first integrals of $L$ are used to reduce the problem into a collection of classical Riemann-Hilbert problems with discontinuous data. 
A. Ainouz, K. Boutarene and A. Meziani
math.AP