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## 14.1.2 Conses as Lists

A list is a chain of conses in which the car of each cons is an element of the list, and the cdr of each cons is either the next link in the chain or a terminating atom.

A proper list is a list terminated by the empty list. The empty list is a proper list, but is not a cons.

An improper list is a list that is not a proper list; that is, it is a circular list or a dotted list.

A dotted list is a list that has a terminating atom that is not the empty list. A non-nil atom by itself is not considered to be a list of any kind---not even a dotted list.

A circular list is a chain of conses that has no termination because some cons in the chain is the cdr of a later cons.

    append      last           nbutlast  rest
    butlast     ldiff          nconc     revappend
    copy-alist  list           ninth     second
    copy-list   list*          nreconc   seventh
    eighth      list-length    nth       sixth
    endp        make-list      nthcdr    tailp
    fifth       member         pop       tenth
    first       member-if      push      third
    fourth      member-if-not  pushnew

Figure 14-3. Some defined names relating to lists.

## 14.1.2.1 Lists as Association Lists

## 14.1.2.2 Lists as Sets

## 14.1.2.3 General Restrictions on Parameters that must be Lists

Copyright 1996-2005, LispWorks Ltd. All rights reserved.