Using include-book you can construct a new logical world by assuming the events in any number of mutually compatible books. Relevant documented topics are listed below. If completed without error, the inclusion of a book extends the logic of the host world by the addition of just the non-local events in the book. You may extend the world by successively including a variety of books to obtain the desired collection of definitions and rules. The desire to compile books is largely responsible for the restrictions we put on the forms allowed in books.
Extensive documentation is available on the various aspects of books.
We recommend that you read it all before using books.