Prolog is a programming language, but a rather unusual one. ``Prolog'' is short
for ``Programming with Logic'', and the link with logic gives Prolog its
special character. At the heart of Prolog lies a surprising idea: don't tell
the computer what to do. Instead, describe situations of interest, and compute
by asking questions. Prolog will logically deduce new facts about the
situations and give its deductions back to us as answers.

Why learn Prolog? For a start, its ``say what the problem is, rather than how
to solve it'' stance, means that it is a very high level language, good for
knowledge rich applications such as artificial intelligence, natural language
processing, and the semantic web. So by studying Prolog, you gain insight into
how sophisticated tasks can be handled computationally. Moreover, Prolog
requires a different mindset. You have to learn to see problems from a new
perspective, declaratively rather than procedurally.
Acquiring this mindset, and learning to appreciate the links between logic and
programming, makes the study of Prolog both challenging and rewarding.

Learn Prolog Now! is a practical introduction to this fascinating
language. Freely available as a web-book since 2002 (see
[...] Learn Prolog Now! has became one of the most
popular introductions to the Prolog programming language, an introduction
prized for its clarity and down-to-earth approach. It is widely used as a
textbook at university departments around the world, and even more widely used
for self study.

College Publications is proud to present here the first hard-copy version of
this online classic. Carefully revised in the light of reader's feedback, and
now with answers to all the exercises, here you will find the essential
material required to help you learn Prolog now.