set the definition body
Major Section:  EVENTS

(set-body foo (:definition foo)) ; restore original definition of foo
(set-body foo foo) ; same as just above
(set-body foo my-foo-def) ; use my-foo-def for the body of foo
(set-body foo (:definition my-foo-def)) ; same as just above
Rules of class :definition can install a new definition body, used for example by :expand hints. See definition and also see hints for a detailed discussion of the :install-body fields of :definition rules and their role in :expand hints.

There may be several such definitions, but by default, the latest one is used by :expand hints. Although the :with keyword may be used in :expand hints to override this behavior locally (see hints), it may be convenient to install a definition for expansion other than the latest one -- for example, the original definition. Set-body may be used for this purpose.

General Form:
(set-body function-symbol rule-name)
where rule-name is either a :definition rune or is a function symbol, sym, which represents the rune (:definition sym).

You can view all definitions available for expansion; see show-bodies.