SLIP (Symmetric List Processing) is a list processing system designed to be added to a higher order language (PL-1 in this version) so that the user has available to him list processing powers. The primary value of such a system is its data handling power. Through SLIP, one can set up lists of data, scan those lists, alter them, and read or write them via external devices with minimal concern for space allotment, data types, or data structure organization. It is possible, for example, to write general programs which create and manipulate list structures whose shape, size, and contents are completely defined only during execution, by the shape, size, and contents of the data. SLIP exists as a set of library subroutines which do the actual manipulations. Thus the user simply writes a normal PL-1 program in which some statements refer to SLIP functions. These subroutines are explained here. (Author/JK)