use Perl

I remember this biting me a few years ago when I was doing text parsing and tagging, before Java 1.5. The project I was working on constantly reminded me of this difference from Perl because I actually had to translate the "prototype" code from C-styled Perl to Java for performance reasons (it was never benchmarked, actually). Sigh.

I went off of your examples and fiddled around a bit more with a reduction operator, and came up with this:

say (([+] @x XeqX @x) - @x.elems)/2;

It appears to work, and doesn't require the diagonal cross operator. The diagonal cross operator does seem like it would be a nice tool to have, tho' :-)