sub Intersection {
    my( $refA, $refB ) = @_;

    my %counts;
    ++$counts{ $1 } while $$refA =~ m[(\S+)]g;

    my $intersects = 0;
    exists $counts{ $1 } and ++$intersects while $$refB =~ m[(\S+)]g;

    return $intersects;
}