A Method for Overlapping and Erasure of Lists An important property of the Newell-Shaw-Simon scheme for computer storage of lists is that data having multiple occurrences need not be stored at more than one place in the computer. That is, lists may be "overlapped." Unfortunately, overlapping poses a problem for subsequent erasure. Given a list that is no longer needed, it is desired to erase just those parts that do not overlap other lists. In LISP, McCarthy employs an elegant but inefficient solution to the problem. The present paper describes a general method which enables efficient erasure. The method employs interspersed reference counts to describe the extent of the overlapping. CACM December, 1960 Collins, G. E. CA601210 JB March 20, 1978 6:33 PM 1024 4 106 1051 4 106 1102 4 106 1132 4 106 1390 4 106 1486 4 106 1549 4 106 1706 4 106 1826 4 106 1878 4 106 378 4 106 2060 4 106 2155 4 106 2168 4 106 2719 4 106 2723 4 106 2838 4 106 2842 4 106 2855 4 106 2879 4 106 3077 4 106 3080 4 106 3106 4 106 627 4 106 106 4 106 106 5 106 106 5 106 106 5 106 1050 5 106 210 5 106 1393 5 106 1549 5 106 2023 5 106 3112 5 106 627 5 106 849 6 106 106 6 106 106 6 106 106 6 106 106 6 106 106 6 106 106 6 106 196 6 106 1051 6 106 1380 6 106 209 6 106 1826 6 106 210 6 106 210 6 106 1878 6 106 296 6 106 1972 6 106 367 6 106 2438 6 106 2723 6 106 2736 6 106 2833 6 106 2838 6 106 406 6 106 627 6 106 627 6 106 731 6 106 731 6 106 731 6 106 753 6 106