[svat]

The 'exact cover' problem has been studied for decades, possibly centuries. The generalization to "primary" and "secondary" items is Knuth's terminology, but the idea itself is a natural one and has been considered before. It is specifically "exact covering with colors" (XCC, not "XC") that is Knuth's innovation/discovery, what a large part of the recent volume discusses, and about which he said there isn't a Wikipedia article yet (because it hasn't caught on yet, and discussed in non-Knuth sources).

[cb321]

Sorry - I meant my "perhaps" to refer to the distinction you reiterated, but I can see why that may not have been clear.

If you feel the (also already mentioned) section on "generalized" exact cover is lacking, hey, it's Wikipedia - anyone can edit it. So, add a little material with alternate / supplementary Knuth terminology / pointers. My intent was merely to point to somewhere to make this material easier to find via search engines (eventually).

[svat]

Ah I see, you were suggesting an existing article on Wikipedia where this information could be added. (It doesn't yet make sense, per Wikipedia policy, to create an article for XCC, for the reasons I mentioned.)

Thanks, I'll look into adding some content to the exact cover article… will have to re-watch Knuth's talk and re-read some of his book/prefascicle sections first!