my @a1 = qw(1 2 5 9 11 12 13);
my @a2 = qw(1 2 5 11 12 13);
my @a3 = qw(1 2 5 7 9 12 13);

my @shared = shared(\@a1, \@a2, \@a3);

sub shared
{
    my $lim = scalar(@_);
    my @lists = map{@{$_}}@_;
    return do{my %seen;
        $seen{$_}++ for(@lists);
        map{delete $seen{$_} if($seen{$_} == 1 || $seen{$_} == $lim)}keys %seen;
        sort {$a <=> $b} keys %seen;
    };
}

##</code><code>##

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