Yep. I notice mention of this additional constraint from another comment. As far as I can tell the article is just incorrect since it misses this constraint up

Yep. I notice mention of this additional constraint from another comment. As far as I can tell the article is just incorrect since it misses this constraint up to that point, unless I'm just a clown and somehow not seeing it. The upside here is that it seems perhaps I wasn't missing the premise, and it was just mis-stated :)