use strict;
use warnings;
my @array1 = ( 1, 2, 5,    9, 11, 12, 13 );
my @array2 = ( 1, 2, 5,       11, 12, 13 );
my @array3 = ( 1, 2, 5, 7, 9,     12, 13 );

use Set::Scalar;
my $x = Set::Scalar->new(@array1);
my $y = Set::Scalar->new(@array2);
my $z = Set::Scalar->new(@array3);

# Either way works.
#my $answer = $x->union($y,$z)
#           - $x->unique($y,$z)
#           - $x->intersection($y,$z);
my $answer = ($x + $y + $z)
           - ($x / $y / $z)
           - ($x * $y * $z);

my @only_two = $answer->elements();