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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. Lists as Association Lists Lists as Sets General Restrictions on Parameters that must be Lists

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