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"Structure and Interpretation of Computer Programs" byHal Abelson, Jerry Sussman and Julie Sussman
(MIT Press, 1984; ISBN 0-262-01077-1),
an excellent computer science text used in introductory courses at MIT.
So called because of the wizard on the jacket.
One of the bibles of the LISP/Scheme world.
Also, less commonly, known as the Purple Book.
from The New Hacker's Dictionary, 2nd edition
(MIT Press, 1993)