Spencer manifolds
  Almost-complex and hyper-complex manifolds are considered in this paper from the point of view of complex analysis and potential theory. The idea of holomorphic coordinates on an almost-complex manifold $(M,\mathbf{J}%)$ is suggested by D. Spencer. For hypercomplex manifolds we introduce the notion of hyper-holomorphic function and develop some analogous statements. Elliptic equations are developed in a different way than D. Spencer. In general here we describe only the formal aspect of the developed theory. 
S. Dimiev, R. Lazov, N. Milev