while (<>) {
  print unless ($_ eq "\n") && ($last ne "\n") && ($secondlast ne "\n");
  $secondlast = $last;
  $last = $_;
}

##</code><code>##

while (<>) {
  $last = $this;
  $this = $next;
  $next = $_;
  print $this unless ($last ne "\n") && ($this eq "\n") && ($next ne "\n");
}
print $next unless ($next eq "\n") && ($this ne "\n"); #last line is special