If the line in the old file does not appear anywhere in newer file, store 0. In doing this, replace the value in the cells associated with the old file with the cell number of the appropriate doubly-linked list. The two cells that were reserved are used as the bounds of the subsequences. Untangle the linked reverse list of the longest common subsequence to become a simple linear list in forward order in the sub-array used for the old file. The values are 0 if the line does not appear in the newer file, or the line number of a candidate match in the newer file.
Skipped numbers are lines that are new in the newer file.
Display the lines that were deleted from the old file, inserted in the newer file, or unchanged.