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use warnings;
use strict;
...
  }
}
close OUT;

    # split BEFORE a ( or AFTER a )
    my @s = split /(?=\()|(?<=\))/;
...
### that even lets you get away with leaving out @s

    push @results, [ split /(?=\()|(?<=\))/ ];

  # display the line if we've never seen the fields
  print OUT @$line if not $seen{$line->[1]}++;