Symbols do not need to belong to a package. For example,
#:plugh will create an "uninterned" symbol named
"plugh" which is a member of no package.
Symbols may also be "in" more than one package (although
they may never have more than one official "home package",
that indicated in their internal
package slot): This
just means that more than one package has an entry for them.
Entering a symbol into a package is called "interning" it in Lisp jargon, presumably because this makes the symbol "internal" to that package.
intern may be used to create an interned
symbol with the given name in the current package: It
returns the existing symbol of that name if such exists,
otherwise creates one and returns it. See section `intern' in Muf Reference.
unintern removes a symbol from the
current package; It can be handy for removing unwanted
variables and functions, perhaps created by mistake.
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