chap lists and arrays revisited figure example of multilist represented by tree figure example of reentrant multilist the shape of the structure is dag (all edges point downwarda list containing sublists will be written as hx hy ha iy ihz ix in this examplethe list has four elements the second element is the sublist hy ha iy and the third is the sublist hz the sublist hy ha iy itself contains sublist if list has one or more sublistswe call multilist lists with no sublists are often referred to as linear lists or chains note that this definition for multilist fits well with our definition of sets from definition where set' members can be either primitive elements or sets we can restrict the sublists of multilist in various waysdepending on whether the multilist should have the form of treea dagor generic graph pure list is list structure whose graph corresponds to treesuch as in figure in other wordsthere is exactly one path from the root to any nodewhich is equivalent to saying that no object may appear more than once in the list in the pure listeach pair of angle brackets corresponds to an internal node of the tree the members of the list correspond to the children for the node atoms on the list correspond to leaf nodes reentrant list is list structure whose graph corresponds to dag nodes might be accessible from the root by more than one pathwhich is equivalent to saying that objects (including sublistsmay appear multiple times in the list as long as no cycles are formed all edges point downwardfrom the node representing list or sublist to its elements figure illustrates reentrant list to write out