sub cardinality
	{
	my $self = shift;

	my $product = 1;

	foreach my $length ( @{ $self->{lengths} } )
		{
		$product *= ( $length + 1 );
		}

	return $product;
	}

##</code><code>##

$self->{lengths}  = [ map { $#{$_} } @$array_ref ];