ANSI Common Lisp 27 Appendix 27.1 Removed Language Features
27.1.1 Requirements for removed and deprecated features
For this standard,
some features from the language described in Common Lisp: The Language have been removed,
and others have been deprecated (and will most likely not appear
in future Common Lisp standards).
Which features were removed and which were deprecated
was decided on a case-by-case basis by the X3J13 committee.
Conforming implementations that wish to retain any removed
features for compatibility must assure that such compatibility
does not interfere with the correct function of conforming programs.
For example, symbols corresponding to the names of removed functions
may not appear in the the common-lisp package.
(Note, however, that this specification has been devised in such a way
that there can be a package named LISP which can contain such symbols.)
Conforming implementations must implement all deprecated features.
For a list of deprecated features, see Section 1.8 Deprecated Language Features.