.Line compare/matching between 2 files.
      "=" edit line cmd compare lines. Open 2 file on each screen split,
      then enclose by "==" the range to be compared.
      Find/eXclude cmd support special search word "*=Mn" for 2 file key
      matching.
         e.g.) f *=M6 10 18.
               col.10-18 is key of the file on the current screen,
               col 6-14 is key of the file on the other screen.
               searches line having col.10-18 which is matching with col 6 of
               2nd file.