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Fungibility is.....
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There has to be universal trust that electronic coins are not being duplicated at will.
There has to be a way to hide personal identity. The coins themselves don't have to be hidden.
It's not rocket science.
Sorry you are conflating separate concerns. Even duplication-at-will doesn't impact fungibility.
Eliding personal identity isn't always necessary for fungibility and it doesn't by itself make fungibility.
I am sorry but you guys are not expert in logic. Smooth is. I am. That is what makes me an excellent programmer.
Avoiding duplication at will is necessary for a currency to be, err, a currency. Logical? Yes; check.
Passing currency from one person to the next without labels to past misdeeds making the currency worthless. Logical? Yes; check.
Cash has no memory of ownership. Logical? Yes; check.
Yeah. I'm right.