Thank you for the peek into the upcoming Exegesis.

...which is now fully on-line.

But I wanted to note that equalness of two undefs is very useful but contradicts with generally accepted laws of three-state logic, does it not?

It sure does. There was a long discussion around that issue on the perl6-language mailing list...starting here.

As I recall, there wasn't a clear outcome to the debate (surprise, surprise), but at the time Larry didn't seem keen on undef taking on the tri-state semantics of NULL.