If the file you want to examine does not fit in memory, you will have to remember two lines at a time.

while (<>) {
  print unless ($_ eq "\n") && ($last ne "\n") && ($secondlast ne "\n"
+);
  $secondlast = $last;
  $last = $_;
}
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update: This doesn't quite work. We'll have to deter deciding whether or not we will print the current line until we have examined the next line.

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 s
+pecial
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