anchor.diff:  { lib
   , fetchurl
   , unzip
  +, gnutar_1-29
  +, brotli_0-4-0
  +, brotli_0-5-2
   }:
   
   { # Optionally move the contents of the unpacked tree up one level.
  
positive.code:     date -d "@$mtime" --utc >&2
    '' + ''
      echo "Building Archive ${name}" >&2
      tar --sort=name --owner=0 --group=0 --numeric-owner \
        --no-acls --no-selinux --no-xattrs \
        --mode=go=rX,u+rw,a-s \
        --clamp-mtime --mtime=@$mtime \
        -c "${name'}" | brotli --quality 6 --output "$out"
      du -bhs "$out"
      cp "$out" "$TMPDIR/${name}"
    '';
  
negative.code:         list = if lib.any (n: item == n) [ "tar" "zip" ] then [ ] else [ item ];
          rest = if item == "tar" then lib.tail rest' else rest';
        in list ++ removeTarZip rest;
  
    versions = {
      "1" = {
        brotli = brotli_0-4-0;
        tar = gnutar_1-29;
      };
      "2" = {
        brotli = brotli_0-5-2;
        tar = gnutar_1-29;
      };
    };
  
    inherit (versions."${version}")
      brotli
      tar;
  
    urls' = (if url != null then [ url ] else [ ]) ++ urls;
  
  