scanning a text file and deleting lines that are double

[theroninwins]

Hey everyone.
My question is a simple one but I somehow got stuck. I have a very large text file with single lines. The text is divided into blocks with an empty line above and one below. How can I compare the lines with eachother line in the same block but not with the others in teh other blocks in that file, and delete everyline that is 2 or 3 times in that block leaving only the first. It shouldn't be that difficult, but somehow I can't get it to work. Hope you can help me on this one.

everyone is there
i am there
everyone is there <- should be deleted
everyone is there <- should be deleted

hello
everyone is there
what is is

[ysth]

Paragraph mode, and unique check (untested):

$/ = "";
while (<IN>) {
   my %seen;
   print OUT grep !$seen{$_}++, split /^/m, $_;
}

[tachyon]

Very snazzy.