diff optimization on specialized files

[Edward Peschko]

hey,

Suppose I had two files with the property such that I knew that:

   - file b contained a superset of lines in file a
   - the lines in file a and file b that were the same were in order.
   - all files in line b that matched line a's were the same or
different (no partial matches or replacements

hence, file a:


line2
line3
line4


and file b

line0
line2
line3
line4
line5


Is there any way/flag that you can tell diff to optimize the above
difference? As it stands, I'm getting spurious replacements in the
diffs outputted. Is there a way to force diff to just show additions
and deletions?

Ed