[Overall] structure of algorithms

The two most common overall frameworks that have traditionally been used in algorithms in computer science are iteration and recursion—and these correspond quite directly to having operations performed respectively in repetitive and nested ways. But while iteration is generally viewed as being quite easy to understand, until recently even recursion was usually considered rather difficult. No doubt the methods of this book will in the future lead to all sorts of algorithms based on much more complex patterns of behavior. (See page 1142.)