chap lists and arrays revisited root figure linked representation for the pure list of figure the first field in each link node stores tag bit if the tag bit stores "+,then the data field stores an atom if the tag bit stores "-,then the data field stores pointer to sublist root figure lisp-like linked representation for the cyclic multilist of figure each link node stores two pointers pointer either points to an atomor to another link node link nodes are represented by two boxesand atoms by circles represented by linked lists pure lists can be represented as linked lists with an additional tag field to indicate whether the node is an atom or sublist if it is sublistthe data field points to the first element on the sublist this is illustrated by figure another approach is to represent all list elements with link nodes storing two pointer fieldsexcept for atoms atoms just contain data this is the system used by the programming language lisp figure illustrates this representation either the pointer contains tag bit to identify what it points toor the object being pointed to stores tag bit to identify itself tags distinguish atoms from list nodes this implementation can easily support reentrant and cyclic listsbecause non-atoms can point to any other node