Ledermann: Complex Numbers
A series of books called the Library of Mathematics were edited by W Ledermann. One of the early texts in the series was Complex Numbers by Ledermann himself. Below we give Ledermann's Preface to the little book taken from the 1960 edition:
The purpose of this book is to present a straightforward introduction to complex numbers and their properties. Complex numbers, like other kinds of numbers, are essentially objects with which to perform calculations according to certain rules, and when this principle is borne in mind, the nature of complex numbers is no more mysterious than that of the more familiar types of numbers. This formal approach has recently been recommended in a Report [The Teaching of Algebra in Sixth Forms, Chapter 3. (G. Bell & Sons, Ltd., London, 1957.)] prepared for the Mathematical Association. We believe that it has distinct advantages in teaching and that it is more in line with modern algebraical ideas than the alternative geometrical or kinematical definitions of i that used to be proposed.
On the other hand, an elementary textbook is clearly not the place to enter into a full discussion of such questions as logical consistency, which would have to be included in a rigorous axiomatic treatment. However, the steps that had to be omitted (with due warning) can easily be filled in by the methods of abstract algebra, which do not conflict with the 'naive' attitude adopted here.
I should like to thank my friend and colleague Dr J A Green for a number of valuable suggestions, especially in connection with the chapter on convergence, which is a sequel to his volume Sequences and Series in this Library.