use Text::xSV;
use Set::Object;

my $parser = Text::xSV->new;

my @keys = split ',', shift(@ARGV);

my @sets;
foreach my $filename (@ARGV) {
    $parser->open_file( $filename );
    push @sets, Set::Object->new;
    $parser->read_header;
    while ($parser->get_row) {
        my $key = join ',', $parser->extract( @keys );
        $sets[-1]->insert( $key );
    }
}

# At this point, you have all the keys in @sets. You can:
#   $union = $sets[0] + $sets[1];
#   $intersection = $sets[0] * $sets[1];
#   $difference = $sets[0] - $sets[1];
#   $symmetric_difference = $sets[0] % $sets[1];
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