Recently I started reading complex analysis again. I remember Feynman once saying that he never understood contour integration but he loved doing integration (the tough ones) by applying the differentiation under integration rule. I found a nice exposition on the same in the Advanced Calculus by Woods, a book that Feynman said he read in his early days. One of the excellent books on Advanced Calculus I have come across. It is a pity that the Publishers (with the exception of Dover Publication) prints these old classics.
I was even surprised when I started searching the book on Complex Variable by E T Copson and found that the book has gone out of print. My enquiry with the Publishers (Oxford University Press) was met with a smug reply that the book is OP. I wonder whether the publishers even have an appreciation the value of these oldies and goldies.
By the way coming back to Contour integration, one limitation I am finding that it is inadequate to solve indefinite integrals. The beauty of the world of complex numbers is the real analysis world transgresses into simpler models once seen through the prism of the Complex world.