Spiegel M., . (1981). Theory and problesm of Complex Variables. : Mc Graw hill; New York.
Spiegel M.R, . 1981. Theory and problesm of Complex Variables. : Mc Graw hill; New York.
Spiegel M.R, . Theory and problesm of Complex Variables. : Mc Graw hill; New York. 1981.