POLYSEG takes as input a list of dotted pairs of numbers. These pairs are assumed to be the co-ordinates of adjacent points along a single closed line. It is further assumed that the x and y co-ordinates of successive points differ by 1, 0, or -1. The output of POLYSEG is a list of dotted pairs of numbers, representing vertices of a polygonal approximation to the figure whose boundary was input. The scale is increased by a factor of four over that of the output; and the output is in fixed or floating point mode; according to the input.