1. Ahlfors, L.V.: Complex Analysis. McGraw-Hill Book Co., New York (1978)
2. Axler, S., Bourdon, P., Ramey, W.: Harmonic Function Theory. Springer, New York (2001)
3. Research Notes in Mathematics;F Brackx,1982
4. Eastwood, M., Penrose, R., Wells, R.: Cohomology and massless fields. Commun. Math. Phys. 78(3), 305–351 (1980)
5. Gilbert, R.P., Buchanan, J.L.: First order elliptic systems, a function theoretic approach. Academic Press, New York (1983)