Ok, z= no longer means z is "equal to" when doing this. The one thing mathematicians do when making this tricky problem work, is change an equal sign to mean "associated with." When they do this, the result -1/12 actually becomes true. So all I have to say about this misleading article is this: Your maths about the 2z=z makes no sense at all. Much smarter people have worked this out and taken the answer -1/12 seriously, so I'm going to listen to them, not some random article.