null: adj., n.
1. adj.
a. (of a list) having no elements: empty. See empty list.
b. (of a string) having a length of zero.
(It is common, both within this document and in observed spoken behavior,
to refer to an empty string by an apparent definite reference,
as in "the null string" even though no attempt is made to
intern2 null strings. The phrase
"a null string" is technically more correct,
but is generally considered awkward by most Lisp programmers.
As such, the phrase "the null string"
should be treated as an indefinite reference in all cases
except for anaphoric references.)
c. (of an implementation-defined attribute of a character)
An object to which the value of that attribute defaults
if no specific value was requested.
2. n. an object of type null (the only such object being nil).
null lexical environment: n.
the lexical environment which has no bindings.
number: n. an object of type number.
numeric: adj. (of a character)
being one of the standard characters 0 through 9,
or being some other graphic character
defined by the implementation to be numeric.