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There is room to which everyone has access. In the room there are visible for all surveillance cameras. Every second recording all available online. The room littered with indestructible piggy bank made of transparent plastic. Like all normal piggy banks, they have a hole in a coin. Everyone can see what each of the coins in piggy banks. No one can make this piggy bank out of the room.

Every person has the key to his piggy bank. Let's say I want to buy your cookies and you are ready to sell them. First, you tell me, which of these is your piggy banks. Then I go into the room wearing a mask. People around the world can see me on surveillance cameras, but can not see my face.

Then I open my piggy bank, pull out the coins and put them in your piggy bank. I leave the room. Now everyone (who needs it, or do not need to) know that your piggy bank has coins that have been in my piggy bank. And so with each transaction. Everyone knows the story of any of the coins.