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| ANSI Common Lisp 14 Conses 14.2 Dictionary of Conses
14.2.33 member, member-if, member-if-not | Function
  Syntax: member item list `&key` key test test-not tail member-if predicate list `&key` key tail member-if-not predicate list `&key` key tail Arguments and Values: item - an object. list - a proper list. predicate - a designator for a function of one argument that returns a generalized boolean. test - a designator for a function of two arguments that returns a generalized boolean. test-not - a designator for a function of two arguments that returns a generalized boolean. key - a designator for a function of one argument, or nil. tail - a list. Description: member, member-if, and member-if-not each search list for item or for a top-level element that satisfies the test. The argument to the predicate function is an element of list. If some element satisfies the test, the tail of list beginning with this element is returned; otherwise nil is returned. list is searched on the top level only. Examples:
       (member 2 '(1 2 3))  (2 3)
       (member 2 '((1 . 2) (3 . 4)) :test-not #'= :key #'cdr)  ((3 . 4))
       (member 'e '(a b c d))   NIL
       (member-if #'listp '(a b nil c d))  (NIL C D)
       (member-if #'numberp '(a #\Space 5/3 foo))  (5/3 FOO)
       (member-if-not #'zerop
                       '(3 6 9 11 . 12)
                       :key #'(lambda (x) (mod x 3)))  (11 . 12)
  Exceptional Situations: Should be prepared to signal an error of type type-error if list is not a proper list. See Also: find, position, Section 3.6 Traversal Rules and Side Effects Notes: The `:test-not` parameter is deprecated. The function member-if-not is deprecated. In the following
       (member 'a '(g (a y) c a d e a f))  (A D E A F)
the value returned by member is identical to the portion of the list beginning with `a`. Thus rplaca on the result of member can be used to alter the part of the list where `a` was found (assuming a check has been made that member did not return nil). Allegro CL Implementation Details: None.

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