sub FishersExactTest2 {
    my @data = @_;
    return unless @data == 4;
    my @C = ( sum( @data[ 0, 2 ] ), sum( @data[ 1, 3 ] ) );
    my @R = ( sum( @data[ 0, 1 ] ), sum( @data[ 2, 3 ] ) );
    my $N =  sum @C;
    my %dividends; $dividends{ $_ }++ for map{ factors $_ } grep $_, @R, @C;
    my %divisors;  $divisors { $_ }++ for map{ factors $_ } grep $_, $N, @data;
    for my $i ( keys %divisors ) {
        if( exists $dividends{ $i } ) {
            $divisors{ $i }--, $dividends{ $i }-- 
                while $divisors{ $i } and $dividends{ $i };
            delete $divisors { $i } unless $divisors { $i };
            delete $dividends{ $i } unless $dividends{ $i };
        }
    }
    my $dividend = product( map{ ( $_ ) x $dividends{ $_ } } keys %dividends );
    my $divisor  = product( map{ ( $_ ) x $divisors { $_ } } keys %divisors  );
    return $dividend / $divisor;
}