We have tried to design this book for both instructional and reference
use, during and after a first course in algebraic topology aimed at
users rather than developers; indeed, the book arose from such courses
taught by the authors. We start gently, with numerous pictures to
illustrate the fundamental ideas and constructions in homotopy theory
that are needed in later chapters. A certain amount of redundancy is
built in for the reader's convenience: we hope to minimize: fiipping
back and forth, and we have provided some appendices for reference. The
first three are concerned with background material in algebra, general
topology, manifolds, geometry and bundles. Another gives tables of homo-
topy groups that should prove useful in computations, and the last
outlines the use of a computer algebra package for exterior calculus.
Our approach has been that whenever a construction from a proof is
needed, we have explicitly noted and referenced this. In general,
wehavenot given a proof unless it yields something useful for
computations. As always, the only way to un- derstand mathematics is to
do it and use it. To encourage this, Ex denotes either an example or an
exercise. The choice is usually up to you the reader, depending on the
amount of work you wish to do; however, some are explicitly stated as (
unanswered) questions. In such cases, our implicit claim is that you
will greatly benefit from at least thinking about how to answer them.