my @C = map { [ $_ ] } @{ shift @_ };

##</code><code>##

  my @C = [];

##</code><code>##

sub cartesian {
    my @C = [];

    foreach (reverse @_) {
        my @A = @$_;

        @C = map { my $n = $_; map { [ $n, @$_ ] } @C } @A;
    }

    return @C;
}