LISP I Programmer's Manual - Software Preservation Group

3. An expression that occurs as a subexpression ofseveral expressions need be represented in storage only once.(2) Construction of List StructuresThe following simple example has been included to illustratethe exact construction of list structures. Two typesof structure are shown, and the recipe for using LISP to deriveone from the other is given.In the list structures below the word 'NIL! is shownin the decrement of the final element of lists and sublists,Strictly speaking in the current 704 representation of liststhis decrement contains zero rather than the indicator NIL whichwould point to the association list for the atomic symbol NIL,but the replacement generally will not affect the user,In the following example we assume that we have alist of the formwhich is represented asIT4/WBI HC I N I L ~ NIL Z 1 N I ~and that we wish to construct a list of the form