Puzzle Paradox Magic

This is for a magic trick called puzzle paradox or block puzzle. The following youtube videos show how it is done. It can also be purchased from most magic trick store.

http://www.youtube.com/watch?v=qCOoXrPmKkc
http://www.youtube.com/watch?v=h-GKOHZc4bQ
http://www.youtube.com/watch?v=QrTMxKkVt1c
http://www.youtube.com/watch?v=vVeLI10f2q4

As you may see in the videos, there are some pieces are confusing and not interchangeable. I changed the dimensions so that b2 and b9 are exactly the same. However, although b4 and b6 look similar, they are actually different and cannot be interchangeable.

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http://www.youtube.com/watch?v=F2b9bkBxUXs